– For years, the U.S. military has sought to distance itself from a brutal civil war in Yemen, where Saudi-led forces are battling rebels who pose no direct threat to the United States.

But late last year, a team of about a dozen Green Berets arrived on Saudi Arabia’s border with Yemen in a continuing escalation of America’s secret wars.

With virtually no public discussion or debate, the Army commandos are helping locate and destroy caches of ballistic missiles and launch sites that Houthi rebels in Yemen are using to attack Riyadh and other Saudi cities.

Details of the Green Beret operation were provided to the New York Times by U.S. officials and European diplomats.

They appear to contradict Pentagon statements that U.S. military assistance to the Saudi-led campaign in Yemen is limited to aircraft refueling, logistics and general intelligence sharing.

There is no indication that the U.S. commandos have crossed into Yemen as part of the secretive mission.

But sending U.S. ground forces to the border is a marked escalation of Western assistance to target Houthi fighters.

Yemen has been convulsed by civil strife since 2014, when the Shiite Muslim rebels stormed the capital, Sanaa. The Houthis, who are aligned with Iran, ousted the government of President Abed Rabbo Mansour Hadi, the Americans’ main counterterrorism partner in Yemen.

In 2015, a military coalition led by Saudi Arabia began bombing the Houthis, who have responded by firing missiles into the kingdom. Yet there is no evidence that the Houthis directly threaten the United States; they have no operations outside Yemen and have not been classified by the U.S. as a terrorist group.

The Green Berets, the Army’s Special Forces, deployed to the border in December, weeks after a ballistic missile fired from Yemen sailed close to Riyadh, the Saudi capital. The Saudi military said it intercepted the missile over the city’s international airport — a claim that was cast in doubt by an analysis of photos and videos of the strike. But it was enough for Crown Prince Mohammed bin Salman to renew a long-standing request that the United States send troops to help the kingdom combat the Houthi threat.