– Russia is intensifying a pressure campaign on U.S. military forces in northeastern Syria following the U.S. withdrawal from much of that area before a Turkish cross-border offensive in the fall, American military and diplomatic officials say.

Russian military personnel have increasingly had run-ins with U.S. troops on highways in the region, breaking agreements between the two countries to steer clear of each other. Russian helicopters are flying closer to American troops. And Wednesday, a U.S.-led convoy returned fire after it came under attack near a checkpoint manned by Syrian government forces, who are backed by Russia.

U.S. officials say these actions by Russian personnel and their Syrian allies are devised to present a constant set of challenges, probes and encroachments to slowly create new facts on the ground and make the U.S. military presence there more tenuous. About 500 U.S. troops remain deployed in Syria with a mission to protect oil fields and help fight ISIS remnants.

The confrontations risk escalating to a significant hostile encounter between Washington and Moscow in the country’s northeast, even as Russian-backed Syrian government troops have stepped up an offensive against rebel enclaves in Idlib in Syria’s northwest.

“We know they’re pressing,” Vice Adm. Tim Szymanski, a Navy SEAL who is deputy head of the military’s Special Operations Command, said in an interview. He echoed the assessment of other government and independent analysts who say the Russians will continue to seek an advantage in the northeast, even in areas patrolled by U.S. and Syrian Kurdish allies and where Russian personnel are not supposed to go.

On Wednesday, a convoy led by U.S. Army soldiers was stopped at a Syrian army checkpoint east of the city of Qamishli. Photos and video on social media, and later confirmed by the Pentagon, showed armored vehicles with U.S., Russian and Syrian flags next to one another. Some residents pelted the U.S. vehicles with stones. Another resident dumped a bucket of dirt on the back of one vehicle. Another tried to light some of the vehicles on fire, according to a Defense Department official.

A brief firefight broke out, with one Syrian man killed. No Americans were killed, but one was slightly injured in the ensuing chaos, the official said.

“After coalition troops issued a series of warnings and de-escalation attempts, the patrol came under small-arms fire from unknown individuals,” said Col. Myles Caggins, a spokesman for the U.S.-led coalition in Baghdad that oversees operation in northeastern Syria. “In self-defense, coalition troops returned fire.”

A Russian defense ministry official said the arrival of Russian troops at the scene made it “possible to prevent further escalation of the conflict,” according to the Tass news agency, a claim that American officials later dismissed.

The encounter drew sharp criticism from Brett McGurk, President Donald Trump’s former special envoy to the coalition fighting ISIS.

“We have American soldiers with an ill-defined mission in Syria (‘protect the oil’) after abandoning three-fourths of once stable territory on Trump’s orders, now forced to navigate roads controlled by Russian and Syrian regime forces,” McGurk said on Twitter. “Too much to ask of our brave warriors.”

In October, Trump abruptly ordered a complete withdrawal of the 1,000 U.S. troops helping Syrian Kurdish forces combat pockets of ISIS fighters, opening the way to a bloody Turkish cross-border offensive. Trump then, just as abruptly, reversed himself and allowed about 500 troops to remain in a much smaller operating zone.

Ever since then, U.S. military officials say, Russia and its Syrian allies have been pushing the boundaries of agreements that Russia and the U.S. reached on whose armies would patrol which territory.