Turkish President Tayyip Erdogan yesterday said a military operation in Syria's Kurdish-controlled Afrin region had begun after cross-border shelling by the Turkish army.

Turkey's army yesterday said it hit shelters and hideouts used by militants from three groups - the Kurdistan Workers' Party (PKK), PYD and YPG, after militants fired on Turkish positions inside Turkey.

"We will destroy the terror corridor gradually as we did in Jarabulus and El-bab operations, starting from the west. Afrin operation has de-facto started in the field. Manbij will follow," Erdogan said.

Erdogan has repeatedly said he would crush the Syrian Kurdish militia in Afrin, which he views as a security threat to Turkey.

Direct military action against territory held by Kurdish militia opens a new front in Syria's civil war and sees Ankara confronting Kurds allied to the United States at a time when Turkey's relations with Washington are reaching breaking point.