(Updates with observatory, rebel source)
BEIRUT, Aug 19 (Reuters) - Syrian air strikes hit near a Turkish military convoy that approached frontlines in northwest Syria on Monday as government forces advanced on a rebel-held town, a monitor and a rebel source said.
There was no immediate comment from Ankara, which backs some of the rebel factions in the northwest and has deployed forces into Idlib province under deals with Russia, Syrian President Bashar al-Assad's most powerful ally.
Syrian state media called the Turkish convoy an act of aggression and said it had entered to help insurgents in the town of Khan Sheikhoun fighting an army advance.
The Syrian Observatory for Human Rights, a UK-based monitoring group that reports on the war, said the convoy was stuck on a highway after air strikes prevented it from continuing southwards. It said a fighter accompanying the convoy was killed.
Overnight, Syrian army troops reached the edges of Khan Sheikhoun in Idlib, a rebel official and a monitor said.
The advance on the town, which has been in rebel hands since 2014, threatens to encircle and expel insurgents from 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 the end of April with Russian help.
The escalation has killed at least 500 civilians and uprooted hundreds of thousands, many stranded near the border with Turkey, the United Nations says.
Turkey, which hosts some 3.6 million Syrian refugees and warns it can not accept more, fears the onslaught in Idlib could spark a new influx.
A series of truces brokered via Russian-Turkish talks have failed to end the fighting in Idlib, where Ankara has a dozen military positions.
A witness and a rebel source from the Turkey-backed Failaq al-Sham faction said the Turkish convoy entered Idlib on Monday but was stopped because of heavy bombing nearby.
Syrian state news agency SANA, citing a Foreign Ministry source, said the Turkish convoy loaded with munitions would not affect "the determination of the Syrian Arab Army to keep hunting the remnants of terrorists".
HEAVY AIR STRIKES
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.
He said there was "international silence" over the surge of violence in Idlib, which he said raised the question of whether world powers had agreed on the offensive.
France called on Friday for an immediate end to the fighting and condemned air strikes on camps for the displaced.
Khan Sheikhoun, along a highway stretching from the capital Damascus to Aleppo city, was bombed with sarin in 2017, an attack that killed dozens of people, wounded hundreds and prompted a U.S. 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.
Pro-government forces were fighting to march into Khan Sheikhoun on Monday, as heavy air strikes hit positions and towns in the south of Idlib, the Observatory said.
The army has closed in on the town from the east and west since a brief ceasefire collapsed earlier this month.
Residents said warplanes pounded the town and nearby villages during the night. (Reporting by Ellen Francis and Tom Perry in Beirut, and Khalil Ashawi in Turkey Additional reporting by Dominic Evans in Istanbul Editing by Alison Williams and Frances Kerry)
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