ISTANBUL — Turkey deployed F-16 fighter jets against government forces in northwestern Syria on Monday, a sharp escalation of the conflict there after six Turkish soldiers were killed by artillery strikes.

President Recep Tayyip Erdogan of Turkey said that as many as 35 Syrian troops had been “neutralized.” The Syrian Observatory for Human Rights, a monitoring group based in Britain, said the number of military personnel killed was at least 13, while state news media in Syria made no mention of any deaths. There were also reports on social media of at least eight civilian deaths when a minibus was struck.

Mr. Erdogan warned Russia, which backs the Syrian government and which controls the airspace in western Syria, not to prevent Turkey from retaliating.

“It should be out of discussion to block us,” Mr. Erdogan said, before leaving for a trip to Ukraine. Describing the dead Turkish soldiers as martyrs, he added that, “It is not possible for us to keep silent” as long as his country’s troops were being targeted.