Republicans in the US House of Representatives have announced plans to introduce a sanctions bill against Turkey for its offensive in Syria.
Congresswoman Liz Cheney said Turkey must face “serious consequences for mercilessly attacking our Kurdish allies” in the region.
It comes as President Donald Trump said he hoped to mediate the conflict.
Turkey moved into northern Syria on Wednesday after the president pulled US troops out of the area.
Critics say the US withdrawal effectively gave Turkey the green light to begin its cross-border assault, which President Recep Tayyip Erdogan says is to create a “safe zone” running for 480km along the Syrian side of the border.
Kurdish militias of the Syrian Democratic Forces (SDF) control the cross-border areas – groups Turkey calls “terrorists” who support an anti-Turkish insurgency.
The SDF have been key allies of the United States in the battle against the Islamic State (IS) group, and say they have been “stabbed in the back” by the US.
There are fears the operation could lead to an ethnic cleansing of Kurds and revive IS.