Turkey denied Russian assertions on Thursday that a ceasefire had been put in place in Syria's Idlib province and demanded Russia restore calm, after the Syrian army and its allies shelled and attacked a Turkish observation post there.
Turkey's Defense Ministry said Syrian government forces had carried out what it assessed to be a deliberate attack, firing 35 mortar shells at one of its observation posts, wounding three Turkish soldiers and damaging equipment and facilities.
Late on Wednesday, the Russian military said Moscow and Ankara had agreed on a full ceasefire in the northwest, centered on Idlib.
However, Turkish Foreign Minister Mevlut Cavusoglu said on Thursday that Ankara would do whatever is necessary if attacks by Syrian government forces continue.
"Right now, it is not possible to say a full ceasefire is in place but our efforts on this with Russia are continuing," Cavusoglu said at a press conference with his French counterpart.
"If these (attacks) continue, we would do what is necessary, nobody should doubt that," he said. "Russia as the guarantor country should put pressure and we expect them to do that... We have serious, sincere efforts about this issue with Russia."
Northwestern Syria is the last part of the country still in control of rebels opposed to President Bashar al-Assad. A de-escalation agreement has been in place in the area since last year, guaranteed by Assad's ally Russia, and by Turkey, which has long supported the rebels.
Turkey has troops stationed at several locations in the area to monitor that agreement.
Ankara has made representations to Moscow about the incident, the defense ministry said.
The Russian Ministry of Defence said it had carried out four air strikes in support of the Syrian military against terrorists in Idlib, the state-run RIA news agency reported.
The de-escalation agreement requires fighters from groups designated as terrorists to withdraw from territory. Syria accuses the rebels of violating it by allowing militants to operate. The rebels say the government is using the presence of fighters as an excuse for a major offensive since April.
Hundreds of thousands of civilians have been forced to flee the area in recent weeks by the worst fighting in months, many of them people who had already been displaced from other parts of Syria during the eight-year civil war.
The Syrian Observatory for Human Rights, a war monitor, said airstrikes on rebel-held areas had paused overnight, but resumed on Thursday morning. They targeted the area around Khan Sheikhoun, an opposition-held town in southern Idlib province, it said, adding that the insurgents had also fired artillery at government forces.
Turkey has pushed Russia to rein in the government's offensive while Russia has said Turkey must curb the jihadist groups that dominate in Idlib.