ANKARA - A convoy of Pro-Syrian government forces entering Syria's northwestern Afrin region turned back after Turkish artillery fire, President Tayyip Erdogan said on Tuesday, adding the convoy was made up of "terrorists" acting independently.

Erdogan said he had previously reached an agreement on the issue with Russian President Vladimir Putin and Iranian President Hassan Rouhani, and warned that the group, which he said were Shi'ite militias, would pay a heavy price.

"Unfortunately, these kind of terror organizations take wrong steps with the decisions they take. It is not possible for us to allow this. They will pay a heavy price," Erdogan told a news conference.