Turkish-backed fighters skirmished Saturday with Kurdish forces in northern Syria, pushing the two U.S. allies in the war against Islamic State extremists closer to an all-out confrontation.

Turkey’s Anadolu news agency said one Turkish soldier was killed and three others were wounded in a rocket attack by a Kurdish militia that the Ankara government has identified as terrorists.

For its part, the Kurd-dominated U.S.-backed Syrian Democratic Forces said its fighters were hit by Turkish jets south of the border town of Jarablus, which was stormed by Turkish forces Wednesday but was reported Saturday to be in the control of the SDF. There were no immediate reports of casualties.

The clashes heightened Western concerns that Turkey’s military incursion into Syrian territory aims to target both IS jihadists and the Kurdish military grouping known as the Kurdish People’s Protection Units, or the YPG militia.

The United States has described the YPG as one of its most effective allies in the fight against IS, while Turkey is demanding a YPG retreat from all border territory seized from IS jihadists.

Men inspect a damaged building after airstrikes on a rebel-held neighborhood of Aleppo, Syria, Aug. 27, 2016.

Aid for Aleppo

In other developments, the U.N.’s special envoy for Syria said the world body had in place an emergency response plan to provide humanitarian relief to the besieged Syrian city of Aleppo, once a temporary cease-fire was in place.

In a statement, Staffan de Mistura said Russia had confirmed that it would honor the proposed U.N. emergency response plan and was seeking the cooperation of the government of President Bashar al-Assad, Moscow’s long-standing ally, for a plan put forward last week.

The U.N. plan is aimed at providing emergency aid to tens of thousands of people trapped in Aleppo, and to restore electricity to the city that was once home to 2.3 million residents.

Separately, monitors from the Britain-based Syrian Observatory for Human Rights said Syrian government helicopters had dropped two explosive-packed barrel bombs minutes apart in the Maadi district of eastern Aleppo.

The strikes were said to have hit near a tent where people were mourning those killed in a barrel bomb attack Thursday in a neighboring district of the once-vibrant city. Fifteen people, including 11 children, were killed in that attack.

The Syrian government has routinely denied using barrel bombs. But analysts point out that Damascus and Moscow command the only forces operating helicopters over Aleppo.

Evacuation of Daraya

Also Saturday, Syrian rebels and their families continued evacuating the long-besieged Damascus suburb of Daraya, as part of an agreement reached late Thursday with the government, after four years of airstrikes and siege left the suburb in ruins.

And in Turkey, suspected Kurdish militants fired rockets at the airport in the main southeastern city of Diyarbakir, sending passengers and staff scrambling for shelter, the Dogan news agency said, but there were no immediate reports of casualties.

Four rockets were fired at a police checkpoint outside the VIP lounge not long before midnight local time, and passengers and staff were taken inside the terminal building for safety, the private news agency said.

Broadcaster NTV said the rockets landed on wasteland nearby.

There were no casualties and no disruption to flights, Diyarbakir Governor Huseyin Aksoy told the news channel.

There was no immediate claim of responsibility.

Kurdish militants have waged a three-decade insurgency in southeastern Turkey.

Some information for this report came from Reuters.