It was a near disaster.

A joint team of elite American special operations troops and Kurdish fighters working together on the ground in northern Syria came under fire from Syrian Su-24 warplanes, prompting urgent calls for help. The U.S. scrambled aircraft to protect the elite forces, raising the prospect that Washington and Damascus could have been in direct combat for the first time.

In the end, the Syrian planes flew off without inflicting any casualties any of the Americans, though local reports said that several Kurds were killed and injured. The U.S. aircraft narrowly missed intercepting the Syrian planes, which had already left the scene near the town of Hasakah, U.S. officials said Friday.

The incident illustrates the dangers faced by some 300 U.S. commandos on the ground in northern Syria advising the Syrian Democratic Forces, a coalition of mostly Kurdish fighters battling the Islamic State. It also raises questions over the level of air support and protection Washington is willing to provide the SDF as they engage with the Syrian army, which is a fight the Obama administration is not interested in engaging in.

In response to the strikes, U.S. military officials contacted their Russian counterparts also operating in Syria, who offered their assurances that their planes weren’t operating in the area. “We made clear that Coalition aircraft would defend its troops on the ground if threatened,” said Marine Maj. Adrian Rankine-Galloway, a Pentagon spokesman said in an email. “The Syrian Regime would be well advised not to interfere with Coalition forces or its partners,” he added.

Soon after the bombing runs, coalition aircraft arrived in response, though the Syrian planes had already departed. It is unclear what aircraft were deployed, but earlier this year, Washington sent F-15 fighters, which specialize in air-to-air combat, to the Incirlik Air Base in Turkey.

The United States will begin increasing air patrols in northern Syria, especially near Hasakah, Pentagon spokesman Capt. Jeff Davis told reporters Friday. “Obviously this is very unusual,” he added. “We’ve not seen the regime take this kind of action against YPG before,” he said, using an acronym for Syrian Kurdish fighters.

There has been some question as to how close to the fighting the American advisors are. In May, a series of photos emerged of U.S. commandos patrolling in the village of Fatisah north of the group’s de facto capital of Raqqa. Just a month prior to that, the Obama administration announced that it was sending 250 more special operators to Syria, to bolster the force of about 50 that were already on the ground.

A Kurdish spokesmen later vowed revenge for Thursday’s attack, raising the possibility of a widening conflict between Syrian troops and Kurdish fighters, who have focused much of their attention on beating back the Islamic State.

Elsewhere in Syria on Friday, two Russian warships operating in the Mediterranean Sea fired volleys of Kalibr cruise missiles at Nusra Front targets in Syria. In October, Russian warships in the Caspian Sea fired 26 Kalibr missiles at targets more than 900 miles away in Syria.