ANKARA, Turkey (AP) — Two Turkish soldiers were killed Thursday by an airstrike in northwestern Syria, according to Turkey’s Defense Ministry, following a large-scale attack by Ankara-backed opposition forces that targeted Syrian government troops.

The deaths brought to 15 the number of Turkish soldiers killed in clashes this month amid a crushing offensive by Syrian President Bashar Assad’s forces aimed at recapturing opposition-held areas in northwestern Syria’s Idlib province.

Intent on halting the advance, Turkish President Recep Tayyip Erdogan had vowed on Feb. 12 to take military action “everywhere in Syria” if another Turkish soldier was killed or wounded.

The multiple front offensive has triggered the biggest single wave of fleeing civilians in Syria’s nine-year war, displacing nearly 1 million people who have rushed toward the Turkish border and are now sheltering in tents or sleeping rough in harsh winter weather.

Thursday’s deaths came after opposition fighters shelled Syrian government forces and entered the village of Nairab, which Assad’s forces had captured Feb. 3. The Turkish Anadolu agency said the fighters destroyed a Syrian tank and armored personnel carrier and seized a second tank.

The Russian military said the militants had launched a massive offensive on Syrian positions near Nairab, under the cover of Turkish artillery, adding that four Syrian soldiers were wounded in the shelling.

“The militants’ actions were supported by the Turkish artillery fire, which allowed the militants to break through the Syrian army’s defenses,” it said.

The military added that at the Syrian military’s request, Russian Su-24 bombers then struck the militants to prevent them from advancing and allowing Syrian government forces to “successfully repel all attacks.”

It was not immediately clear whether it was the Russian airstrikes that killed the two Turkish soldiers.

A Turkish Defense Ministry statement posted on Twitter said as many as 50 Syrian government soldiers were killed and that five tanks, two armored personnel carriers and other equipment were destroyed.

The exchange marked a serious escalation that risks escalating into a full-blown conflict between Turkey and Syria. Erdogan has called on Assad’s forces to retreat from Idlib or face an “imminent” Turkish attack.

It also comes amid faltering talks between Turkish and Russian officials on restoring calm to the Idlib area.

Turkey and Russia back opposing sides in Syria’s civil war. The Syrian government’s recent campaign against the rebel-held Idlib stronghold has strained cooperation between Moscow and Ankara and led to direct clashes between Syrian and Turkish troops recently.

Turkey maintains observation posts in northern Syria that were set up to monitor a 2018 cease-fire agreement with Russia. It sent in thousands of additional troops and armored vehicles in recent weeks and has threatened to attack Assad’s forces.

“We are delivering our final warnings. We have not reached the desired results as yet,” Erdogan said Wednesday. “The operation in Idlib is a matter of time. We could enter (Idlib) suddenly one night.”

Anadolu reported earlier that opposition fighters attacked Syrian government forces and entered the the village of Nairab, which the troops had captured Feb. 3. It said the opposition forces began advancing toward Nairab after Syrian government targets there were hit by artillery fire. They destroyed a tank and an APCbelonging to Syrian forces and seized a second tank, according to the report.

Syrian opposition activists confirmed the report, saying Turkey-backed insurgents stormed the village of Nairab near the strategic town of Saraqeb, both of which were captured by Syrian troops earlier this month.

The Britain-based Syrian Observatory for Human Rights, a Syria war monitor, reported casualties on both sides. It wasn’t immediately clear if Turkish troops took part in the attack.

Syrian state TV reported that government forces have repelled the attacks on Nairab.

Turkish Foreign Minister Mevlut Cavusoglu said Russian and Turkish delegations would hold more talks on reducing tensions in Idlib province and that the Turkish and Russian leaders could meet too, if necessary.

“It is true that at the moment, there are differences in the (two sides’) positions,” Cavusoglu told state broadcaster TRT. The delegations narrowed their differences a bit but “are not yet at the point we want” to be, he said.

Turkey and Russia have closely coordinated their moves in recent years in Idlib province. A truce reached between the two countries collapsed in late 2019, leading to the current Syrian offensive, backed by Russia.

Russian officials have said they hold Turkey responsible for the collapse of the cease-fire deal, saying Ankara had not held up its end to rein in militants who continued attacking Syrian and Russian targets.

Isachenkov reported from Moscow. Associated Press writer Bassem Mroue in Beirut contributed.