Tillerson arrived in Turkey on Thursday for two days of what officials said would likely be uncomfortable discussions between the allies.
He met with Erdogan for more than three hours in Ankara, as part of what was widely expected to be the most difficult leg of a five-day regional visit, Reuters reported.
The two sides’ relations have frayed over a number of issues, particularly US support for the Syrian Kurdish YPG militia, seen as terrorists by Turkey.
Turkey launched an air and ground assault last month in Syria’s northwestern Afrin region to drive the YPG from the area south of its border.
Ankara considers the YPG to be an arm of the PKK, a banned group that has waged a decades-long insurgency in Turkey.