ANKARA, Turkey – U.S. Vice President Joe Biden apologized Saturday to Turkish President Recep Tayyip Erdogan, who was angry over comments in which Biden said Erdogan had admitted that Turkey had made mistakes by allowing foreign fighters to cross into Syria.

Biden spoke with Erdogan by phone on Saturday, the White House said.

“The vice president apologized for any implication that Turkey or other allies and partners in the region had intentionally supplied or facilitated the growth of ISIL or other violent extremists in Syria,” the White House said, referring to an acronym for the Islamic State group.

The spat comes as Turkey, a NATO ally, is expected to define the role it will play in the U.S.-led coalition against the Islamic state militants who have captured a swath of Iraq and Syria.

Responding to questions following his speech at the Harvard Kennedy School on Thursday, Biden described Erdogan as “an old friend.” Biden added: “He (Erdogan) said: ‘You were right. We let too many people through.’ Now they’re trying to seal their border.”

Erdogan said: “I have never said to him that we had made a mistake, never. If he did say this at Harvard then he has to apologize to us.”