Like some ghostly spectre their convoy of trucks appeared out of the dust thrown up by the desert. Within minutes they had pulled up on the roadside next to us. The ageing vehicles were heavily laden, packed with bags and bedding on top of which sat men in paramilitary uniforms layered in fine dun coloured dust and cradling assault rifles and rocket propelled grenade launchers.

At first sight they were a rough looking and intimidating bunch, most either sullen or hyped up having just spent weeks on the frontlines of the small Iraqi city of Tal Afar notorious for sectarian hatred and slaughter.

“Hashd al-Shabi,” announced my Arabic speaking colleague ominously, referring to the Iraqi Shi’ite Popular Mobilisation Units (PMU) to which these fighters belonged. Their identity was further borne out by the huge flags and banners draped from their vehicles depicting Iraqi cleric Grand Ayatollah Ali al-Sistani and a few of his Iranian counterparts.

Despite their gruff appearance the men turned out to be an affable lot, engaging openly in conversation with the two Western journalists they had unexpectedly stumbled across en-route to the Iraqi city of Mosul, where they were to reinforce others fighting the Sunni jihadists of the Islamic State (IS) group.

Looking back on that encounter a few years ago it was not a meeting I’d like to repeat right now in light of the volatile events played out these past days.

For it’s hard to imagine such fighters being well disposed towards Westerners at this moment after the US drone strike on Thursday that killed PMU leader Abu Mahdi al-Muhandis alongside Major General Qasem Soleimani, the Iranian mastermind behind such militia units.

As the long-term head of Iran’s Islamic Revolutionary Guard Corps Quds Force (IRGC) and the architect of nearly every significant operation by Iranian intelligence and military forces over the past two decades, it’s frankly hard to overstate the importance of Soleimani’s assassination at the hands of the US.

“More than anyone else, Soleimani has been responsible for the creation of an arc of influence - which Iran terms its ‘Axis of Resistance’ - extending from the Gulf of Oman through Iraq, Syria, and Lebanon to the eastern shores of the Mediterranean Sea,” Ali Soufan, a former FBI agent and national security analyst, wrote in a 2018 profile.

Soleimani who once described himself as “the smallest soldier,” might have been short in stature quiet in demeanour and possessed what one US journalist described as an “underrated charisma,” but the man who survived the horrors of trench warfare in the Iran-Iraq conflict of the 1980’s was a force to be reckoned with.

Other than US antipathy towards the 62-year old Soleimani, perhaps no country had more cause to fear and despise the Iranian general and his Quds force pernicious influence in the Middle East than Israel.

It’s a measure then of the Jewish State’s recognition and obsession with Soleimani that on his birthday last March, the Israel Defence Force (IDF tweeted a video of a layered cake with moving images of birthday greetings from all of Iran’s proxies ranging from Hezbollah to Hamas.

As the video comes to an end the cake explodes after being hit by Israeli missiles, a message of clear intent from Iran’s arch nemesis.

That the Americans appear to have beaten the Israelis in delivering Soleimani’s coup de grace, will not trouble the regime of Israeli Prime Minister Benjamin Netanyahu one bit.

‘Job done,’ will be the prevailing mood in Jerusalem, even if Israel will now be bracing itself for the expected retaliatory backlash from Tehran.

Curiously though given that the Israelis themselves have had Soleimani in their crosshairs many times before and not acted, it does the beg the question as to why the Americans chose this particular moment to strike the killer blow.

If Washington’s explanation is to be believed, then Soleimani was already doing the rounds of his proxies plotting more attacks on US targets like the missile strikes that killed a US civilian contractor and wounded several American troops at an Iraq base in Kirkuk.

“Soleimani was plotting imminent and sinister attacks on American diplomats and military personnel but we caught him in the act and terminated him,” Trump told reporters at his Mar-a-Lago resort in Florida on Friday. “We took action last night to stop a war. We did not take action to start a war.”

That Soleimani was perceived to be an enemy of the US and a terrorist neither Republicans nor Democrats disputed. Certainly none mourned his death, but some were also united in expressing concern over the existence of intelligence suggesting that more attacks on US interests were imminent and that Trump’s order to act unilaterally would move the US closer to an intractable war with Iran.

This after all was the very war the president insisted in the wake of Soleimani’s assassination that he was trying to “stop”.

As House of Representatives Intelligence Committee Chairman Adam Schiff, a Democrat, questioned, why would Trump chose now to act against Soleimani, when previous administrations decided such a step would increase the risks in the region?

“If the administration has a broader strategy, they have yet to articulate it,” Schiff told reporters.

And therein lies one of the crucial questions right now when it comes to US policy in the Middle East. Just what, if any strategy, does the Trump administration have short of jumping to the orders of a gaff prone Commander in Chief.

This to be clear is a US president who, far from extracting America from the quagmire of conflict in the region and bringing “our boys” home, only further embroils Washington at every turn.

“With respect to Iran, the assassination is a strategic error entirely of Trump’s own making,” observed Stephen M Walt, professor of international affairs at Harvard University, writing yesterday in the influential US- based Foreign Policy magazine.

“Egged on by Saudi Arabia, Israel, hawkish institutes like the Foundation for Defence of Democracies, and some of his wealthy backers, the president abandoned the multilateral agreement that has successfully capped Iran’s nuclear programme and also created a diplomatic opening that a savvier administration could have used to address Iran’s regional activities,” Walt added, summing up the frustrations of many US Middle East watchers.

In addition Walt points out, Trump has also embarked on a comprehensive programme of economic warfare against Iran that has sought to force the country to change its foreign policy to suit Washington and perhaps even to topple the regime there, despite Trump’s insistence to the contrary.

If recent US polls are anything to go by the American public are equally wary of Trump’s motives. According to a University of Maryland poll conducted in September last year of a nationally representative sample of respondents, overwhelmingly, the US public does not believe that US interests warrant war with Iran. Even among Republicans, only 34 per cent say that war should be on the table to protect American interests. These figures too were compiled before the latest assassination of Soleimani for which the tactical justification remains questionable.

As for Tehran itself, it has already made clear it will not kowtow to such pressure from the Trump administration, not least given that in many quarters Soleimani was publically revered in Iran.

Which brings us to the other question on everyone’s lips concerning just what the scale and shape of Tehran’s response might be?

Until now, Iran’s response has been robust but calibrated. A sequence of rockets aimed at the US presence in Iraq throughout the autumn was more nuisance than menace, though clearly the attack that killed an American contractor near Kirkuk has shifted that calibration. As one observer noted, Iran has many retaliatory weapons at its disposal “from hackers to Hezbollah.”

Ironically, in great part because of Soleimani’s own efforts in mobilising the intelligence and military assets of the Revolutionary Guards Quds Force of which he was chief, Iran would not be starting from scratch in mustering its response.

“What the Iranians have in front of them is a menu of potential routes they could take. It could be directly or indirectly,” says Naysan Rafati, an Iran analyst at the International Crisis Group (ICG).

In recent years Iranian hackers have erased the computer servers of Saudi Arabia’s state-owned oil company Aramco, breached the networks of dozens of US banks and been accused of trying to meddle in the 2020 presidential election.

Aggressive cyber attacks offer Tehran one potential weapon for striking back globally but this is far from being the only international weapon in its arsenal. In the past when necessary, the Quds Force has been behind the orchestration of attacks against targets ranging from Latin America to Eastern Europe and South Asia.

It’s also been linked to numerous plots in Western countries, including in Belgium, Denmark, France, the US and the UK in recent years. But it’s in the Middle East that any retaliatory efforts will most likely be concentrated.

“In its immediate neighbourhood, Iran could put together a response almost immediately, such as last week’s assault on the US Embassy in Iraq,” says Nick Rasmussen, former director of the US National Counterterrorism Centre.

“In the broader Middle East, it might take Iran more time, but its proxies could still threaten US personnel, business people or tourists, Rasmussen told NBC News.

Iran's strong presence in Lebanon through Hezbollah makes the possibility of retaliation against US targets there a distinct possibility. Hezbollah exercises influence in large swaths of Lebanon, including parts of Beirut, and has the capability to launch attacks against US targets in the country.

Likewise in Yemen, Iran could push Houthi rebels there to launch retaliatory attacks against US allies as well, even though Iran does not directly control that group.

The Houthis maintain a robust arsenal of drones as well as ballistic and cruise missiles, which they have used to carry out attacks in Yemen, Saudi Arabia and surrounding waters such as the Bab el-Mandeb strait. Potential targets include, but are not limited to, airports, critical infrastructure, energy infrastructure, military targets and vessels transiting the Red Sea.

As the online American geopolitical intelligence platform Stratfor has highlighted, it’s barely four months since the attacks on the Abqaiq and Khurais oil-processing facilities that took half of Saudi Arabia's oil production down. While Houthi rebels claimed responsibility, many analysts pointed to Iran as being behind the strike given its degree of sophistication.

And then of course there is Iraq on whose soil Soleimani was killed. Even before his death the risk was already high that Iranian backed Iraqi militias like the PMU’s would attack US and Western forces assets and potentially, commercial interests. During many visits to Iraq in recent times I’ve seen for myself the growing influence of those PMU’s and the fighters within their ranks like those I met on the road that day a few years ago near Mosul.

While some Iranian-backed militias led by leaders like Abu Mahdi al-Muhandis who was killed with Soleimani on Thursday are not popular among many Iraqis, US moves to stoke a conflict with Iran on Iraqi soil has already injected serious diplomatic tension into Baghdad's relationship with Washington and fuelled nascent efforts in the Iraqi parliament to re-evaluate Iraq's security cooperation with the United States.

All of this does not bode well for the on-going fight against the jihadists of the Islamic State (IS) group which far from being a spent force, show signs of re-galvanising themselves in Iraq. It’s anybody’s guess whether for example the Iraqi security forces will continue to work with the Americans in this vital role. One can only wonder if such crucial factors were taken into full consideration when Trump gave the order for Thursday’s assassination of Soleimani.

As a recent report on Iran’s regional strategy by security think tank The Soufan Centre concluded, Tehran has long developed a “playbook” under the supervision of Soleimani to “build pro-Iranian armed factions into political movements with progressively increasing influence and capabilities.”

For the moment there is great uncertainty over what precisely Iran will do next. But one thing is certain, that “playbook” will now be opened and retaliation is coming. What form it takes could well determine the course of the Middle East for months and years to come. Donald Trump might still rue the day he gave that order to assassinate Qasem Soleimani.