A team of elite US soldiers called the Green Berets were deployed in secret last year to the Saudi Arabia-Yemen border to help defeat the Houthi rebels.

Since the Yemen conflict began three years ago, Houthi rebels have launched ballistic missiles towards Riyadh and other Saudi Arabian cities on numerous occasions and the kingdom has responded with its own airstrikes. Twelve Green Berets were deployed to the border in December 2017 just weeks after Saudi Prince Mohammed bin Salman renewed his call for American support claimed the kingdom had intercepted the latest missile, shot at the Riyadh airport.

Officials from President Donald Trump’s administration as well as European and Arab diplomats, told the New York Times the troops are “helping locate and destroy” training sites and missiles of the Houthis. Part of their mission is to also train Saudi troops on how best to defend their border with Yemen.

The newspaper reported that the rebels “pose no direct threat to the US”. The Pentagon had previously said its role in the conflict was limited to “refuelling, logistics, and general intelligence sharing”.

The war in the region's poorest country began in 2014 when Houthi rebels took control of Sanaa and pushed south towards Aden. Saudi Arabia and its coalition, fearing that the rebels were being backed by its rival Iran, then launched a series of air strikes to restore control for the government of President Abd-Rabbu Mansour Hadi.

The Houthis, who hail from northern Yemen, control Sanaa and much of the country's north - which borders Saudi Arabia - and the key Hodeida port on the Red Sea coast.

Since the air strikes began, at least 10,000 people have died as a result and 40,000 have been wounded. The conflict has also played a large part in causing a cholera epidemic and leaving millions facing famine and severe malnutrition.

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“There is no indication that the American commandos have crossed into Yemen as part of the secretive mission,” the newspaper reported and the Pentagon have cited security reasons for not commenting on the matter save to say that the operation includes “limited non-combat support, such as intelligence sharing,” according to Major Adrian Rankine-Galloway.

Democratic Senator Tim Kaine, a member of the Armed Services Committee, called the Green Berets mission a “purposeful blurring of lines between train and equip missions and combat”. He has renewed his call for Congress to pass a new “authorisation of use of military force” (AUMF), since the US Congress is the only body that has the ability to declare war. The US has been operating in several conflict zones around the world under the same AUMF since 2001, which were war powers passed just days after the September 11th attacks when the US military began its ongoing war in Afghanistan.

The situation in Yemen Show all 14 1 /14 The situation in Yemen The situation in Yemen Houthi supporters trample on a US flag during a gathering mobilizing more fighters into several Yemeni battlefronts, in Sana'a, Yemen EPA The situation in Yemen People carry the coffins of men, who were killed in the recent Saudi-led airstrikes during their funeral, in the Old City of Sanaa, Yemen AP The situation in Yemen Pro-government fighters give food to Yemeni children on the road leading to the southwestern port city of Mokha. Yemeni rebels are putting up fierce resistance in a key Red Sea port city where they are encircled by pro-government force Getty Images The situation in Yemen A Yemeni stands in front of a graffiti protesting US military operations in war-affected Yemen, in Sana'a, Yemen. According to reports, US Special Forces troops allegedly disembarked from US helicopters in the Yemeni town of Yakla and attacked several houses belonging to members of the terrorist group Al-Qaeda, killing three high-ranking Al-Qaeda members and nine civilians, six women and three children. One American serviceman has been killed and three injured in the attack EPA The situation in Yemen US Special Forces troops allegedly disembarked from US helicopters in the Yemeni town of Yakla and attacked several houses belonging to members of the terrorist group Al-Qaeda, killing three high-ranking Al-Qaeda members and nine civilians, six women and three children. One American serviceman has been killed and three injured in the attack EPA The situation in Yemen A Yemeni female fighter supporting the Shiite Huthi rebels, and carrying weapons used for ceremonial purposes, takes part in an anti-Saudi rally in the capital Sanaa Getty Images The situation in Yemen Yemeni female fighters supporting the Shiite Huthi rebels, and carrying weapons used for ceremonial purposes, take part in an anti-Saudi rally in the capital Sanaa Getty Images The situation in Yemen A boy shouts slogans next to pro-Houthi fighters, who have been injured during recent fighting, during a rally held to honour those injured or maimed while fighting in Houthi ranks in Sanaa, Yemen Reuters The situation in Yemen Balls of fire and smoke rise from a Houthi-held military camp following alleged Saudi-led airstrikes, in Sana'a, Yemen EPA The situation in Yemen Yemenis search under the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa Getty Images The situation in Yemen A Yemeni boy looks on as Yemenis search under the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa Getty The situation in Yemen A Yemeni boy sits amidst the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa AFP/Getty The situation in Yemen Marine One with US President Donald Trump flies with a decoy and support helicopters to Dover Air Force Base in Dover, Delaware, for the dignified transfer of Navy Seal Chief Petty Officer William 'Ryan' Owens who was killed in Yemen Getty Images The situation in Yemen US President Donald Trump aboard the Marine One to greet the remains of a US military commando killed during a raid on the al Qaeda militant group in southern Yemen on Sunday, at Dover Air Force Base, Delaware, US Reuters

There are also US intelligence experts in the southern Saudi city of Najran that have been working with Saudi troops.

Despite Mr Trump’s ever-closer ties to Saudi Arabia, he had asked the kingdom to end a blockade on Yemeni ports last December, possibly around the time the Green Berets had been deployed.