A bomb planted on a public bus in the northwest Syrian town of Afrin killed three civilians and wounded about 20, several witnesses told Reuters on Sunday.

The blast came on the first anniversary of Operation Olive Branch, an air and ground assault by Turkey on the mainly-Kurdish Afrin to drive out the Syrian Kurdish YPG militia.

Turkish President Recep Tayyip Erdogan said it and similar attacks "will never discourage our fight in Afrin."