Prime Minister Tayyip Erdogan said on Thursday Turkey could act against a "terrorist" organisation in northern Syria if it sees it as a threat, referring to outlawed Kurdish militants.

Recep Tayyip Erdogan's comments Thursday follow reports that Kurdish rebels and the Democratic Union Party of Syria took control of five cities along the Syrian-Turkish border.

"We will not allow a terrorist group to establish camps in northern Syria and threaten Turkey," Erdogan told a news conference.

"If there is a step which needs to be taken against the terrorist group, we will definitely take this step," he said.

Syrian President Bashar al-Assad and those close to him were about to leave power and preparations are underway for a "new era" in Turkey's southern neighbour, Erdogan said before departing for London.