Turkish president Recep Tayyip Erdoğan sought to play down a bitter rift with the US after a meeting with Donald Trump at the White House.
Turkey has previously expressed its anger over Washington’s decision to arm Syrian Kurdish fighters, who Ankara consider are a terrorist group.
It also wants the US to extradite religious leader Fethullah Gulen who is accused of being behind a failed military coup last year.
However, the two leaders pledged continuing co-operation against ISIL, a foe recognised by both.
“Today we face a new enemy in the fight against terrorism,” Trump declared.
“Again, we seek to face this threat together… We offer our support to the Turkish nation.
“We support Turkey in the first fight against terror and terror groups like ISIS and the PKK and ensure they have no safe quarter, the terror groups.”
Turkey has been a crucial partner in the US-led coalition against Islamic State forces in Syria.
Historically it has also played a key role as a Nato ally.
Prior to the dispute over the role of Kurdish groups in the region, Trump and Erdogan had showed signs of mutual admiration, standing out among world leaders in hailing each other’s victories in domestic votes.