Turkish reprisals killed 31 Syrian soldiers in the battleground northwestern province of Idlib on Friday after a bombardment Ankara blamed on Damascus killed 33 Turkish soldiers, a monitor said.

The retaliatory drone and artillery strikes hit Syrian army positions in southern and eastern parts of the province which were recaptured by the government in a nearly three-month-old offensive against the rebel enclave, the Syrian Observatory for Human Rights said.

At least 27 regime fighters died in those strikes, while another four were killed by artillery fire on positions in neighbouring Aleppo province, the Observatory added.

Also on Friday in Idlib, four members of a single family, two of them children, were killed in air strikes, according to the Britain-based monitor, which relies on a network of sources inside Syria.

There was no immediate confirmation from Damascus of the reported troop deaths.

But a source at the foreign ministry criticised Turkish President Recep Tayyip “Erdogan’s forces involvement in the fight alongside... terrorist groups”, a catch-all term used by the regime for rebel and jihadist groups operating in Syria.

The Syrian army “will carry out its duties in eliminating the terror presence in all Syrian territory”, the source added.

The flare-up has prompted NATO to call an urgent meeting of its ruling council.

The alliance on Friday offered solidarity and support to Turkey but no pledges of concrete new measures to defend Ankara’s forces.

Turkey had said it retaliated “from the air and ground” for the deaths of the 33 soldiers, Ankara’s biggest single loss of personnel by far since it launched its intervention in Syria in 2016.

The deadly strike comes after weeks of growing tension between Turkey and Russia—the main foreign brokers in the Syrian conflict.

The latest casualties bring to 53 the number of Turkish soldiers killed in Syria this month alone.

The flare-up came after Turkish-backed rebels reentered the key crossroads town of Saraqeb in Idlib province.

The town had been one of the most significant gains of the government offensive earlier in February because it lies along the M5 highway that connects Syria’s four largest cities.

A Syrian military source quoted by the state news agency SANA had accused Ankara on Thursday of actively supporting the groups that retook Saraqeb.

The Observatory said that Turkish artillery fire was helping the rebel factions in Saraqeb resist regime efforts to wrest back the town on Friday.