A Syrian government helicopter was downed in a rural area west of Aleppo in Syria's Idlib region on Friday, with conflicting claims over who was responsible.
Turkey's state-owned Anadolu news agency said the helicopter was shot down by Turkish-backed rebels while Russia's state-owned Russia Today channel said it was hit by a shoulder-fired missile launched from a Turkish military observation post near the town of Dara Azza.
The Syrian Observatory for Human Rights, a UK-based war monitor, blamed the attack on Turkey. It said both pilots were killed.
There was no immediate claim of responsibility.
A rebel military source and eyewitnesses told Reuters that Russian jets had been targeting areas in the countryside west of Aleppo earlier on Friday, but they returned to the city after the helicopter was downed.
Turkey has threatened to respond harshly to threats to its forces in Idlib in the face of a government offensive to reclaim Syria's last major rebel stronghold after nearly nine years of civil war.
A government helicopter was downed earlier this week after an attack by Syrian forces that killed five Turkish soldiers, the second such deadly confrontation following an attack that killed eight Turkish personnel on February 3.
The Syrian government campaign, backed by Russian air strikes, has raised tensions between Russia and Turkey, which supports some opposition groups. Both countries accuse each other of failing to honour a ceasefire agreement for Idlib and adjoining rebel-held areas that they agreed upon in late 2018.
Syrian President Bashar Al Assad's forces have retaken significant territory since launching a stepped-up offensive in December, including areas around some of the Turkish military posts set up to monitor the ceasefire agreement.
Turkey sent thousands of troops and heavy weaponry across it border into Idlib in the past two weeks, saying it was strengthening its position to respond to further attacks and enforce the ceasefire.
The fighting has driven nearly 800,000 people from their homes since December 1, including 140,000 in the space of three days this week, according to the UN. About 60 per cent of them are children.
The humanitarian situation for people in north-west Syria is “at the most critical points”, the UN said in a briefing on Thursday.
“This level of displacement couldn’t come at a worse time as more and more people are squeezed into an increasingly smaller area of land with little more than the clothes on their back,” said David Swanson, UN regional spokesperson for the crisis in Syria.
Mr Swanson described people fleeing in the middle of the night to avoid detection in temperatures below zero.
“The crisis is deepening by the minute, but the international community remains indifferent,” he said.
Government forces have focused their offensive on areas along a strategic highway that runs through opposition territory and connects the country’s south to the north. The M5 highway, now secured by Syrian troops, had been out of government control since 2012 and accessing it was part of a now failed 2018 ceasefire agreement.