Iran’s nuclear ambitions have not surprisingly been bitterly opposed by Saudi Arabia, the Gulf region’s most powerful Sunni state, with the result that both countries are now engaged in fighting a proxy war for supremacy throughout the Arab world.

^{Yemenis and members of the Houthi militia inspect the scene of a suicide attack a day after it targeted a Houthi mosque in Sana'a, Yemen}

And nowhere is this bitter dispute more keenly felt than in Yemen, a nation that holds the unwelcome distinction of being the Arab world’s poorest state. For decades Yemen was regarded by most Arabs as Saudi Arabia’s back garden, such was the influence the Saudi royal family had brought to bear on Yemen’s internal political and economic affairs since the 1930s.

In particular Riyadh demonstrated its stranglehold over Yemeni politics by supporting the rise to power in 1978 of Ali Abdullah Saleh as the country’s powerful president, and then helping in 1990 to negotiate the second reunification of a country that includes the former British protectorate of Aden.

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Under Saleh’s rule Riyadh generally enjoyed cordial relations with the Yemeni government in Sana’a. But two key developments have dramatically changed this cosy arrangement during the past decade. The emergence of al-Qaeda in the Arabian Peninsula (AQAP), an off-shoot of Osama bin Laden’s original terror Sunni-based movement which was founded by a group of Saudi dissidents, helped to provoke ethnic, tribal and social tensions that quickly returned the country to a state of open civil war.

These tensions, moreover, were further exacerbated by Iran’s decision to support the Houthi rebels, the Shia minority in the north of the country, a decision that has helped to further destabilise the country after President Saleh was forced from office in the wake of the original Arab uprisings in 2011.

For the past four years the Quds force of Iran’s Revolutionary Guards have been smuggling weapons to the Houthis, as well as providing expert military training, with the result that the Shia Houthi militia finally succeeded in seizing control of the capital Sana’a last year, forcing the Western-backed president, Abed Rabbo Mansour Hadi, to seek refuge in Aden.

Last week it was claimed that Tehran was increasing its support for the Houthis with the delivery of a 185 ton shipment of weapons and other military equipment.

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The Iranian-backed takeover of northern Yemen certainly represents a major setback for the Saudis, who have a 1,000-mile porous southern border with the Yemenis to protect. The establishment of a pro-Iranian, Shia regime in Sana’s has also been met with deep resentment by the country’s militant Sunni population, which in recent months has seen AQAP - once regarded as the region’s most deadly terrorist organisation by Western intelligence agencies - being replaced by supporters of the Sunni fundamentalist Islamic State (Isil) movement, which in the past year has seized control of large swathes of northern Iraq and Syria.

While there have been reports of tensions between Isil and Aqap, there can be little doubt that Sunni extremists were behind this week’s deadly suicide bomb attacks in Yemen, which were deliberately targeted as Shia mosques in the country frequented by Houthi militiamen, who comprised the majority of the victims.

^{An injured Yemeni boy sits in a wheelchair is surrounded by adults in a hospital in Sana'a, Yemen (YAHYA ARHAB/EPA)}

There will inevitably be speculation that the Saudis were in some way involved in the atrocities, particularly as the suicide attacks coincided with the Houthis mounting aerial bombing raids against the Aden headquarters of President Hadi.

The group that claimed responsibility for the attacks, the previously unknown Sana’a branch of Isil, justified its action by claiming “Infidel Houthis should know that the soldiers of Islamic State will not rest until they eradicate them...and cut off the arm of the Safavid (Iranian) plan in Yemen.” No one in Riyadh is going to argue with that.

The Saudis have certainly proved adept at protecting their interests against Iranian incursions in the past. When Iran tried to provoke Shia dissidents in the tiny Gulf state of Bahrain to overthrow the kingdom’s Sunni monarchy, the Saudi military quickly intervened to crush the protest movement.

Whether the Saudis initiate a similar military operation in Yemen will depend to an extent on the outcome of the talks currently taking place between the U.S. and Iran over the future of its nuclear programme. U.S.

President Barack Obama is said to be keen to cut a deal with Iranian President Hassan Rouhani, who yesterday claimed that the talks were taking positive strides and that “there is nothing that cannot be resolved.”

But the talks are being viewed with deep scepticism by the Saudis and other countries in the region, including Israel, which fear that Mr Obama is preparing to do a deal that would allow Iran to retain the technical capability to develop nuclear weapons, even if Tehran gives commitments not to do so.

And if that is the outcome then the Saudis will want to have a nuclear deterrent of their own, with the result that a conflict that is currently being fought with proxies might one day escalate in an all-out nuclear war between Sunnis and Shias.