CIA chief David Petraeus is visiting Turkey for meetings on regional issues, a US official told AFP on Monday.
The official would not say with whom the CIA chief would be meeting and where.
According to local media, Petraeus arrived in Istanbul on Sunday and his meetings with Turkish officials on Monday would focus on the Syrian crisis and anti-terror fight.
Turkish and US officials last month held their first operational planning meeting aimed at bringing about the end of Syrian President Bashar al-Assad's embattled regime.
During that meeting, the two parties discussed contingency plans in the case of potential threats including a chemical attack by Assad's regime, as well as the threat of armed groups including outlawed Kurdistan Workers' Party (PKK) and Al-Qaeda which could exploit a power vacuum in Syria.
This is the second visit to Turkey by the CIA chief who held closed-door talks with Prime Minister Recep Tayyip Erdogan and Turkish intelligence chief Hakan Fidan in March.