In the distance plumes of black smoke spiralled high into the sky. Suddenly the intercom on board the US Blackhawk military helicopter on which I was travelling crackled into life.

“That’s Fallujah sir. Believe me you don’t wanna go there,” said the crew chief sitting next to me.

The year was 2007, and I was en route from the Iraqi capital Baghdad to the town of Baquba, whose reputation as a hotbed of Islamist insurgent activity was surpassed only by that of the infamous Sunni enclave of Fallujah.

Sitting just 32 miles west of Baghdad on the Euphrates River, Fallujah dates from Babylonian times. In more recent years however this “city of mosques” as locals call it, has often been at the epicentre of the wider battle for Iraq.

Known to Americans as the site of the costliest battle of the Iraq War back in 2004, Fallujah today is once again the battleground on which all eyes are trained.

For the last few weeks, Iraqi government forces, backed by US and coalition airstrikes, have launched a military offensive to recapture the city from the Islamic State (IS) group who overran it more than two years ago.

Fallujah is only one of many frontlines right now that is seeing an intensification of the battle against IS across the Middle East.

In neighbouring Syria, the US-backed Syria Democratic Forces coalition, a collection of mostly Kurdish militias has launched an offensive encroaching on the IS stronghold of Raqqa.

Meanwhile, in far off Libya where a new, UN-backed government of national unity has taken up power in Tripoli after two years of deadlock, the fight back against IS has also been stepped up.

As in Iraq and Syria, British and US special forces have been deployed alongside local fighters on the Libyan frontlines.

It was thought to be either Special Air Service (SAS) or Special Boat Service (SBS) commandos that intervened recently destroying an IS vehicle packed with explosives after it sent Libyan fighters fleeing in panic on Shaddadah Bridge, some 50 miles south of the city of Misrata.

Some reports suggest the British troops fired a Javelin missile into the vehicle.

For the moment however it is the Iraqi city of Fallujah on which the world’s attention is focused. There the stakes are high for the government of Iraqi Prime Minister Haider al-Abadi.

“Zero hour for the liberation of Fallujah has arrived. The moment of great victory has drawn near and Daesh has no choice but to flee,” said al-Abadi on his official Twitter feed, using an Arabic acronym for the jihadist group.

On the face of it, militarily the decision to retake Fallujah makes little sense, with the priority being to wrest back control of Iraq’s second largest city, Mosul. It also fell to IS two years ago and in effect remains the de-facto capital of their self-proclaimed caliphate in Iraq.

But if the Fallujah offensive makes little sense militarily it does make for an astute political move by Iraqi Prime Minister Haider al-Abadi, who has been under intense pressure over the past month.

Since the end of April activists loyal to Muqtada al-Sadr, the prominent Shia cleric and militia leader, have twice breached the heavily fortified “green zone” and parliament in Baghdad in protest against corruption and sectarianism.

The capital too has been rocked by a series of bomb attacks in predominately Shia areas of the city, the devices and IS bombers thought to have come from Fallujah.

Sensing the political pressure under which al-Abadi’s government is buckling, IS has been doing all it can to stir up sectarian hatred and division between Shias and Sunnis.

Not surprisingly then al-Abadi needs to be seen to take the IS bull by the horns, and the Fallujah operation provides just that opportunity.

But just what will the battle for Fallujah involve? What are the implications for both the Iraqi government and IS when it is retaken and what too does it mean for the civilian population caught in the crossfire?

For now it is estimated that some 20,000 Iraqi military personnel are involved in the operation.

In the lead up to the offensive against the city these forces laid siege before slowing moving into outlying urban areas. With IS heavily dug in at the heart of the city this will doubtless lead to ferocious house-to-house fighting.

Having held Fallujah for so long IS clearly know the terrain and with their backs to the wall and few places to which they can retreat are expected to put up a determined fight. Already though the jihadists may have received a major setback with reports that an American airstrike has killed its top commander in Fallujah. According to Colonel Steve Warren, the US military spokesman in Baghdad, an airstrike Wednesday targeting the IS headquarters in the city killed Maher al-Bilawi, also known as Wilayat Fallujah.

The airstrike was “a result of intelligence that we gathered on the headquarters and his location,” said Warren. “And we had the opportunity to take the strike and we took it.”

He said al-Bilawi’s death “won't completely cause the enemy to stop fighting, but it's a blow. And it creates confusion and it causes the second-in-command to have to move up. It causes other leadership to have to move around.”

Maher al-Bilawi who was not considered a “high-value target” by the US was nevertheless believed to be in command of the estimated 500-1,000 IS fighters in Fallujah. Those fighters, say military analysts, will have no hesitation in booby-trapping mosques, hospitals and using civilians as human shields. They will also maximise the propaganda value of those civilians killed by government forces, knowing how problematic this was for al-Abadi’s regime after it retook the neighbouring city of Ramadi in a previous offensive. Though a military victory was achieved there, Ramadi was all but totally laid to waste.

Similarly during the siege of the town of Tikrit last year, there were reports of widespread looting and arson in the city, which local politicians blamed on the Iranian-backed militias.

Around Fallujah last week, Iranian Revolutionary Guards Quds Force commander General Qassem Suleimani showed up in photos with senior militia commanders taken at an operations room outside the city. He is allegedly assisting those militias in the Fallujah assault.

All too aware of such a controversial presence and how any heavy handedness could wreck progress in terms of sectarian reconciliation, al-Abadi visited a military field headquarters just east of Fallujah on Thursday, calling on security forces to advance with care.

“The armed forces and the brave fighters, their duty is to protect civilians from this terrorism, from random killing, from torture,” al-Abadi stressed.

While his government ground troops have sought to open corridors for trapped residents, few civilians have been able to escape. IS snipers and minefields have effectively closed off most routes.

Jasim al-Halbusi, a member of the Anbar provincial council’s security committee, said IS fighters had erected blast walls on one of the bridges leading out of the city to keep people in.

But desperate residents he added were also hesitating to take any available exits for fear of what lay on the other side in the shape of Iranian backed forces and Shiite militias.

“They are between two fires,” was how Halbusi described their terrible dilemma.

Humanitarian groups have already warned of a possible bloodbath if forces backed by Iran enter mostly-Sunni Fallujah, even though the militia have given assurances they will remain mostly outside the city and leave the main attack to government forces.

Over the last few days Iraqi aircraft dropped leaflets over the city urging residents to leave and telling those who couldn’t to put white sheets on their roof to protect them from attack by government forces. Some of the 50,000 residents still in the city have heeded the advice.

However as, US military spokesman Colonel Warren pointed out, most likely IS fighters would do the same on their own fighting positions.

“This is an enemy that doesn't want the civilian population to leave," said Warren. “Why? Because they want to hide behind the civilian population. They know it makes it harder for us.”

The UN says it now has reports of people dying of starvation and being killed for refusing to fight for IS. We have reports of an increase in the number of executions of men and older boys,” said Melissa Fleming, a spokeswoman for the UN High Commissioner for Refugees.

“Other eyewitnesses say a number of people attempting to depart have been executed, or whipped. One man's leg was amputated reportedly.”

The UN's humanitarian agency, said that around 10,000 families were unable to leave the besieged city and were in “a very precarious situation.”

Since last week, 800 people have reached safety, mostly from outlying areas, and some families report having to walk for hours under harrowing conditions to reach safety.

“IS gave us food that only animals would eat," said one woman Umm Omar, speaking of her time inside Fallujah. Along with 10 members of her family she had chosen to take a chance and slip out of the city.

“We are now receiving distressing reports of civilians trapped inside Fallujah who are desperate to escape to safety but can’t," said Lisa Grande, the United Nations Humanitarian Coordinator for Iraq. "Food supplies are limited and tightly controlled. Medicines are exhausted and many families have no choice but to rely on dirty and unsafe water sources.”

The latest crisis in Fallujah has only added to the already enormous humanitarian challenge posed by the war in Iraq.

The UN estimates that 10 million people in the country need some form of humanitarian assistance, including 3.4 million people who have been displaced since January 2014. An additional three million people are thought to be living under IS control.

Humanitarian partners estimate that $300 million is needed by July to sustain first-line emergency response across the country.

This weekend the air strikes, mortar salvoes and gunfire continue, as does the trickle of civilians able to get out. Most regional observers believe it is only a matter of time before Fallujah is back in government hands.

That its retaking will have any effect on the IS bombing campaign in Baghdad is anyone’s guess. Some US intelligence officials are resigned to the fact that as IS loses territory, almost inevitably it will return to its old terrorist methods and tactics. That itself will not be much comfort to long-suffering Baghdadis.

For the moment also it will matter little to those civilians trapped inside Fallujah. Back in 2007 little did I think that almost a decade later the city of mosques would still be war torn place few would think of setting foot. What the full cost of Fallujah’s retaking will be in human terms is still to play out.

On a more cynical political and strategic level there are those within the US military who are concerned that the Fallujah offensive is little more than a face-saving operation for beleaguered Prime Minister al-Abadi.

They fear also that Fallujah is nothing more than a costly distraction that will delay the much more significant assault on Iraq’s second largest city Mosul, the headquarters of IS.

Should that prove successful say some strategists, it might finally break the back of IS in Iraq. The Mosul operation will prove to be an enormous military undertaking. If past experience and the current situation in Fallujah is anything to go by the human cost and humanitarian fallout too will be even more nightmarish.