While relations between Washington and its main Muslim ally in NATO have been strained by a number of issues, Turkey has been particularly infuriated by U.S. support for the Syrian Kurdish YPG militia, which it sees as terrorists.
The US has around 2,000 military personnel in northern Syria supporting the SDF, which is an alliance of militias in northern and eastern Syria and largely dominated by the Kurdish People’s Protection Units (YPG).
Erdogan said this week that Turkish forces would sweep Kurdish fighters from the length of Syrian border and could push all the way east to the frontier with Iraq, a move that would risk a possible confrontation with U.S. forces allied to the Kurds.
“In the Afrin area, we had actually gotten to the point where humanitarian aid was flowing, refugees were coming back in … The Turkish incursion disrupts that effort,” U.S. Defense Secretary Jim Mattis said.
Turkey views the Kurdish People’s Protection Units (YPG), an offshoot of SDF, a terrorist organization linked to the homegrown Kurdish Workers’ Party (PKK) militant group, which has been fighting for independence inside Turkey.