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 killed was at least 13. The Turkish leader also 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. Syrian government forces […]