Turkish and U.S. Presidents Recep Tayyip Erdogan and Joe Biden began meeting on the sidelines of the G20 summit in Bali, the Turkish leader's office said.

"President Erdogan began talks with U.S. President Biden on the margins of the G20 Leaders Summit in Bali," the office said.

Experts assess the meeting as "critical," as official Ankara had earlier publicly rejected U.S. condolences for the terrorist attack in Istanbul, and Erdogan himself accused Biden of hiding the Islamic preacher Fethullah Gulen, with whom Turkey links an attempted coup in the country in 2016.