NO sooner had Air Force One touched down in Riyadh last week than the tell-tale signs were all there.

As US President Barack Obama came down the steps from his private Boeing 747 at King Khalid International Airport, the make up of the reception committee said a lot about the state of US relations with Saudi Arabia.

There to greet Obama was Prince Faisal bin Bandar bin Abdulaziz Al Saud, the governor of Riyadh. King Salman meanwhile was a few miles away busy greeting senior Gulf officials arriving for the Gulf Cooperation Council summit.

In the Arab World such gestures speak volumes. The decision to send a lower-ranking official to greet the US President made clear that the House of Saud was less than pleased with its long-time ally.

In some ways the snub was to be expected. Often described as one of Washington’s worst kept secrets, it’s been said that President Obama would prefer to have little truck with the leaders of Saudi Arabia. Realpolitik of course dictates otherwise.

For his part, Obama knew he was flying into a diplomatic sandstorm last week. In a recent interview with Atlantic magazine he outlined some of the hardest foreign policy decisions he has had to make while in office.

Saudi Arabia, he pointed out, needed to learn to “share” its Middle East neighbourhood with its arch-rival Iran. Needless to say, it was an observation that did not go down well in Riyadh.

Other things too are not going down well with the Saudis. To begin with there is the brewing controversy over fresh information that has surfaced appearing to link Saudi Arabia and the September 11 attacks in 2001 that gave rise to the so-called War on Terror.

It has been revealed that the flight certificate of al-Qaeda bomb maker Ghassan Al-Sharbi was discovered hidden in an envelope from the Saudi embassy in Washington when they arrested him in 2002.

In light of this, Obama is facing increasing calls to declassify a 28-page section of a Congressional report that many believe will point to Saudi involvement in the 2001 plane hijackings.

Allied to this there is also the ongoing efforts in the US to pass a Senate bill that

would allow families of those killed in the 9/11 attacks to sue the Saudi government.

Riyadh’s response to the possibility of that bill being passed has been robust to say the least.

Last month Adel al-Jubeir, the Saudi foreign minister, delivered the kingdom’s message personally during a trip to Washington, telling politicians that Saudi Arabia would be forced to sell up to $750 billion in treasury securities and other assets in the United States before they could be in danger of being frozen by American courts.

Some analysts are sceptical that the Saudis will follow through with such a move, insisting that such a sell-off would be difficult to execute and would end up crippling the kingdom’s economy. Either way, it is yet another sign of the escalating tensions between Riyadh and Washington.

Though tensions may be running high this has not stopped arms sales between the two nations from flourishing. Under the Obama administration sales have expanded to such a level that last week two US senators introduced a resolution that would put restrictions on American arms exports to the kingdom.

“I’m arguing for a rethink, people notice our hypocrisy in the Middle East when we talk about our values and it seems to drop low on the list in priorities,” said Senator Chris Murphy of Connecticut, who along with Republican Senator Rand Paul of Kentucky, introduced the bill setting new conditions on US military aid to Saudi Arabia.

The push for the legislation comes as the death toll continues to rise in Riyadh’s year-long intervention in Yemen, and requires that the president certify that Saudi Arabia is demonstrating an effort to “minimize harm to civilians” and “facilitate humanitarian assistance before Congress can consider the sale or transfer of air-to-ground munitions to Saudi Arabia.”

These US senators are not the only ones concerned about arms sales to Saudi Arabia.

In the first six months of last year Britain sold £1.75bn-worth of weapons to the kingdom at a time when Riyadh and it allies were escalating airstrikes in Yemen.

Inside the country itself the main fight is between forces loyal to the beleaguered President, Abdrabbuh Mansour Hadi, and those allied to Zaidi Shia rebels known as Houthis.

Officials in Riyadh blame the Houthis for being Iran’s proxy in the region and Saudi Arabia is determined to deny bitter rival Iran sway over another Arab capital.

Led by Riyadh a coalition comprising of five Gulf Arab states and Jordan, Egypt, Morocco and Sudan have escalated their aerial bombardment. The UN now estimates that at least 3,200 civilians have been killed and 5,700 wounded, with 60 per cent of the casualties inflicted as a result of the air campaign.

Perhaps the greatest unintended consequence of this Saudi-led military offensive with US backing is that it has allowed al-Qaeda in the Arabian Peninsula (AQAP) to thrive and consolidate its grip.

AQAP now has a significant presence across at least a quarter of central Yemen. It also controls about 370 miles of Yemen's coastline. Here al-Qaeda fighters have abolished taxes for local residents and operate speedboats manned by RPG-wielding fighters who impose fees on ship traffic.

If the Islamic State (IS) group’s capital is the Syrian city of Raqqa, then al-Qaeda’s is Mukalla, a south-eastern Yemeni port city of half a million people.

As well as seizing the bank deposits, AQAP has extorted $1.4 million from the national oil company and earns up to $2m every day in taxes on goods and fuel coming into the port. Just as IS seized the central bank in Mosul in northern Iraq, AQAP looted Mukalla’s central bank branch, hauling in an estimated $100m.

“That represents their biggest financial gain to date,” one senior Yemeni official is quoted a saying. “That’s enough to fund them at the level they had been operating for at least another 10 years.”

According to one local resident who spoke to journalists: “The group is experiencing a period of obscene, unprecedented wealth and luxury.”

AQAP regularly shows propaganda videos online or posts pictures of its fighters repairing damaged bridges and paving streets in Hadramout and other cities under its control.

All the money for such work it insists comes from groups such as Guardians of Sharia or Sons of Hadramout, names AQAP has taken on as part of a rebranding effort to emphasise its local origins. Paving roads or restocking local hospitals all plays out well with some local residents.

“I prefer that al-Qaeda stay here, not for Mukalla to be liberated,” one 47-year-old resident is reported to have told local journalists.

“The situation is stable, more than any ‘free’ part of Yemen. The alternative to al-Qaeda is much worse,” the man is said to have insisted, expressing the fears of many over the factional fighting that continues to grip other parts of the country.

Such remarks from ordinary civilians will be of real concern to those fearful of AQAP’s increasing influence in Yemen.

For some time now the world has been preoccupied with the Islamic State group, in Syria and Iraq. But al-Qaeda’s gains in Yemen are the first time it has controlled and administered territory on this scale. The Islamists are said to have as many as 1,000 fighters in Mukalla alone.

But if the Yemeni civil war and Saudi Arabia’s intervention in it offer AQAP many opportunities, they also pose many pitfalls and could dramatically shift the jihadist’s strategies in ways they have long sought to avoid.

AQAP has always been somewhat different from other al-Qaeda affiliates in that it has been determined to strike outside Yemen and the Middle East, even making attempts inside the United States and Europe.

This, it should be remembered, is the same AQAP that was behind the Charlie Hebdo massacres and numerous bomb plots, its operatives having previously trained in Yemen.

The question now it that given its territorial gain inside Yemen, will the group start focusing more of its attention there and in the region? Also having a dramatic impact on its strategy will be the fact that it is operating amid an all-out civil war. While on the one hand this can provide safe havens for terrorists, war zones can be dangerous for terrorists as well as civilians.

Yemen has many armed and large warring factions, and it will be hard for AQAP to stay neutral, as it must protect its supporters and guard its own areas of operations.

Some intelligence analysts too point to the fact that if al-Qaeda manages to successfully root itself as a political and economic organisation in parts of Yemen, it could become a more resilient threat, much like al-Shabaab in nearby Somalia.

Last but not least in assessing what comes next for AQAP in Yemen is the question of Saudi policy.

Saudi policies have never been easy to read, but the unpredictability has risen steeply in recent months, Saudi watchers say.

On the one hand, Saudi Arabia opposes al-Qaeda in general and AQAP in particular, as the latter has targeted Saudi security forces and, in 2009, even tried to kill Prince Mohammed bin Nayef, who is now in charge of Saudi military operations in Yemen.

On the other hand, Saudi Arabia has a history of working with Salafi-jihadi groups and may believe they are the lesser of two evils in the war against the Houthis, whom the Saudis believe are in the pay and sphere of influence of Tehran.

Could it be that Riyadh sees expediency in aiding all the Houthis’ enemies even if that means AQAP?

One year on, it still remains unclear just who is winning the war in Yemen. Saudi Arabia and its coalition partners claim to have regained control of more than 80 per cent of the country, but the Houthis hold sway in the key strongholds of Sanaa, Ibb, and Taiz.

With each unlawful coalition airstrike, it becomes more evident that Saudi Arabia and its allies either do not care about respecting international humanitarian law or are incapable of adhering to its fundamental rules.

Britain, the United States, and France meanwhile continue to authorise lucrative arms deals with that same Saudi-led coalition. There is no doubt that President Obama was snubbed last week by the House of Saud, and relations between Washington and Riyadh are as sour as they have ever been. Make no mistake about it however, when it comes to the flow of arms and military materiel, its business as usual.

While it would be wrong to talk in terms of winners and losers amidst all this cynical diplomatic horse-trading, one thing is clear – Al-Qaeda stands to gain most and it will be ordinary Yemeni citizens who will bear the consequences.