The situation has since been de-escalated, a military spokesman said.

American Coalition forces on patrol in Syria exchanged small arms fire with unknown individuals near a pro-regime checkpoint while on patrol in north eastern Syria, with the situation now de-escalated, a military spokesperson said.

The troops were on patrol near Qamishli, by the Turkish-Syrian border, when they encountered a checkpoint occupied by pro-Syrian regime forces on Wednesday.

“After Coalition troops issued a series of warnings and de-escalation attempts, the patrol came under small arms fire from unknown individuals,” Operation Inherent Resolve spokesperson Col. Myles B. Caggins III said in a statement. “In self-defense, Coalition troops returned fire. The situation was de-escalated and is under investigation.”

The Coalition patrol has since returned to their base, he added.

The group who opened fire on the U.S. were regime supporting locals, and Syrian State media has reported that a man was killed by U.S. troops in the exchange of fire, according to the Associated Press.

The exchange of fire highlights the tense and complex situation for the remaining U.S. forces in northeastern Syria where Russian and Syrian government forces occupy various checkpoints.

The U.S. pulled out the majority of their troops in the region, leaving just a few hundred behind to protect key oil fields. Coalition troops continue to conduct missions against ISIS in Syria, where the terror group has pockets of fighters looking to reconstitute.

Fighting in the war-torn country has intensified in recent weeks as regime forces, backed by Iranian proxies and Russian air power, have closed in on reclaiming Idlib, the last rebel stronghold in the country in the northwest. More than half a million Syrians are believed to have been displaced by the conflict in the last two months, and U.S. officials are concerned about a refugee crisis.

To complicate the situation further, the assault on Idlib has seen Russian-backed Syrian forces clash with Turkish forces and Turkish-backed militias, who have crossed into various points in northern Syria as part of military incursion against the Kurds.

Last week James Jeffrey, the U.S. special envoy for Syria, singled out the Russian role in the unfolding humanitarian crisis.

“We’re seeing much more aggressive Russian action in Idlib” and at the United Nations to boost Assad, he told reporters. “Russia apparently feels that it cannot bring the regime to do the necessary things to bring it in line with the international community’s expectations, so the Russians are going to press forward on a military victory.”

Jeffrey will meet with Turkish officials today after President Erdogan said Tuesday that the Syrian regime would pay a “very heavy price” for their role in the fighting in Idlib.

But while the U.S. has stepped up its condemnation if the joint Syrian-Russian assault on Idlib, National Security Adviser Robert O’Brien has said that the U.S. won’t act as the “world’s policeman.”

“What are we supposed to do to stop that?” he told the Atlantic Council Tuesday. “We’re supposed to parachute in as a global policeman and hold up a stop sign and say, ‘Stop this Turkey, stop this Russia, stop this Iran, stop this Syria’?”