US Defense Secretary Jim Mattis urged Turkey on Tuesday to show restraint in its offensive against a Kurdish militia in Syria.
"We take very seriously Turkey's legitimate security concerns and we are committed to work with our NATO allies on those," Mattis said in Jakarta at the start of an Asian tour.
"We urge Turkey to exercise restraint in the military action and the rhetoric."
Turkey's President Recep Tayyip Erdogan has vowed to step up an offensive against Kurdish targets in neighbouring Syria and in Iraq.
The operation, which includes an air and ground campaign involving Ankara-backed Syrian rebels, aims to oust the People's Protection Units (YPG) from Afrin in northern Syria.
Turkey views the YPG as a terror group and an offshoot of the Kurdistan Workers' Party, which has long fought for autonomy within Turkey.
The YPG denies aiming for separatism.
Turkey's offensive is complicated by the US relationship with the YPG, on which it relied to help oust Islamic State jihadists from their Syrian strongholds.
"The violence in Afrin disrupts what was a relatively stable area in Syria and distracts from the international effort to defeat ISIS," Mattis said Tuesday, using another name for the Islamic State.
"We are calling all parties to remain focused on defeating ISIS."