Turkey on Thursday threatened to use force against "radicals" in Syria's Idlib province after Russia accused Ankara of failing to "neutralise" jihadist groups under a 2018 deal. "Force will be used in Idlib against those who do not abide by the ceasefire, including the radicals," Defence Minister Hulusi Akar was quoted as saying by the official Anadolu news agency.

"Any form of measure will be taken," he said. Idlib - the last opposition bastion in Syria - is held by an array of rebels dominated by the Hayat Tahrir al-Sham (HTS) jihadist group, which is led by members of the country's former Al-Qaeda franchise.

President Bashar al-Assad's forces have pressed ahead with an offensive in the region since December, killing more than 380 civilians, according to the monitoring group the Syrian Observatory for Human Rights. The killing of 14 Turks in Idlib in government shelling has fuelled tensions between Ankara and Damascus, while raising stakes with Russia - a key ally of Assad.

President Recep Tayyip Erdogan on Wednesday accused Russia of committing "massacres" in Idlib and threatened to strike government forces anywhere in Syria if the slightest harm is done to Turkish troops. In return, Moscow accused Ankara of failing to honour the 2018 deal, with Kremlin spokesman Dmitry Peskov saying the Turkish side "had taken upon itself an obligation to neutralise terrorist groups" in Idlib.

Under the bilateral agreement, radical groups were required to withdraw from a demilitarised zone in the Idlib region. As Turkey and Russia traded accusations over the escalation in Idlib, US special envoy for Syria James Jeffrey held closed-door talks with Turkish officials in Ankara on Wednesday.

Washington has thrown full support for its NATO ally's response to the Syrian government fire in Idlib. Jeffrey, in comments published Thursday on the official Twitter account of the US Embassy in Turkey, voiced US support for Ankara's "legitimate" interests in Syria. "Our job is to convince (Russia, Iran and the Assad government) that they are not going to have a military victory," he said.