Nine other troops were also wounded in northwest Syria’s Idlib province after they came under heavy artillery fire from the Syrian government Sunday, according to a Turkey defense department statement.

Turkish President Recep Tayyip Erdogan said up to 35 Syrian government soldiers had been killed Monday in response, and pledged further retaliation.

Children bearing the brunt of latest escalation in Syrian civil war

Erdogan said up to 40 Syrian targets were being considered as part of the operation, and warned Russia — the most powerful backer of Syrian President Bashar al-Assad — to “not stand in our way.”

“We told the Russian authorities you are not party to this it is totally the regime and do not stand in our way. Because we have martyrs, we cannot remain silent. We will continue to respond, including with our F-16s, our howitzers, our artillery, it is all in the field firing on the targets determined by our national intelligence,” Erdogan said.

Turkish soldiers are in the last rebel-held area of Syria as part of a 2018 de-escalation agreement between Ankara and Moscow. The Syrian government has mounted an aggressive air campaign in Idlib in recent weeks, amassing troops along strategic highways leading to the rebel enclave.

On January 12, Russia and Turkey announced a ceasefire that has failed to end the violence.

A Turkish military convoy of passes through the Syrian town of Dana on February 2.

The recent violence has pushed people out of multiple towns. Syria announced the capture of the opposition-held city of Maraat Al Nouman on Thursday.

UNICEF estimates that more than 300,000 people have been displaced since December and that 1.2 million children are in desperate need.

The Syrian government and Russia deny targeting civilians and say they are targeting terrorists, pointing to the dominance of Hayat Tahrir Al Sham (HTS), a former al Qaeda affiliate, in the area.