BEIRUT - Air strikes hit positions near a Turkish convoy which was stuck at a highway in northwest Syria after crossing into Idlib province on Monday, the Syrian Observatory for Human Rights said.
The British-based war monitoring group said one fighter from a Turkey-backed faction accompanying the convoy was killed and others were injured.
Syrian state media said the convoy entered Syria on Monday to help insurgents in the town of Khan Sheikhoun who are fighting a government advance, calling it an act of aggression.
The "aggressive" move would not affect "the determination of the Syrian Arab Army to keep hunting the remnants of terrorists" in the town in Idlib province or elsewhere, state news agency SANA cited a Foreign Ministry source as saying.
There was no immediate comment from Ankara, which backs some of the rebels in the northwest and has deployed forces into the Idlib region under deals with Russia, President Bashar al-Assad's most powerful ally.
Syrian army troops reached the edge of Khan Sheikhoun in the south of Idlib province overnight, a rebel official and a monitor said. The advance not only threatens the town, in rebel hands since 2014, but also to encircle insurgent fighters in their only patch of territory in neighbouring Hama province.
The northwest is the last major stronghold of the opposition to Assad, whose military has been waging its latest offensive there since late April with Russian help.
The surge in violence since late April has killed at least 500 civilians and uprooted hundreds of thousands, many towards the Turkish border, the United Nations says.
A witness said a Turkish military convoy, with rebel allies, entered Idlib on Monday but was stopped because of heavy bombing there.
Syrian state news agency SANA, citing a Foreign Ministry source, said the convoy loaded with munitions would not affect "the determination of the Syrian Arab Army to keep hunting the remnants of terrorists" in Khan Sheikhoun or elsewhere.
Colonel Mustafa Bakour of the Jaish al-Izza rebel faction said battles raged on the outskirts of the town. Fighters arrived to reinforce the frontline, he said, including some from the National Army, a Turkey-backed rebel force based further north near the border.
Khan Sheikhoun, along a main highway stretching from the capital Damascus to Aleppo city, was bombed with sarin in 2017, an attack that killed dozens on people, wounded hundreds others and prompted a US missile strike.
An investigation by the United Nations and the Organisation for the Prohibition of Chemical Weapons blamed the attack on the Syrian government. Damascus denies using such weapons.
Since a brief ceasefire collapsed this month, the Syrian army has closed in on Khan Sheikhoun from the east and west.
Pro-government forces arrived at the northwest flank of the town under heavy air strikes and were fighting to march into it, the Syrian Observatory for Human Rights said.
Residents said warplanes pounded the town and nearby positions during the night.