The State Department urged Turkey to exercise restraint on Sunday after Turkish ground forces advanced into northern Syria and clashed with the Kurdish militia in the area.
"We urge Turkey to exercise restraint and ensure that its military operations remain limited in scope and duration and scrupulous to avoid civilian casualties," State Department spokeswoman Heather Nauert said in a statement.
"We call on all parties to remain focused on the central goal of defeating [the Islamic State in Iraq and Syria]. Now is the time for great nations to work together to secure a peaceful stability for the people of Syria."
Turkish forces moved into the Afrin region of northern Syria on Sunday and pounded surrounding areas with artillery fire and airstrikes.
Turkey is targeting the U.S.-backed YPG, a Syrian-Kurdish militia it considers to be a terror organization.
“Our jets took off and started bombing. And now the ground operation is underway. Now we see how the YPG ... are fleeing in Afrin,” Turkish President Recep Tayyip Erdoğan said, according to Reuters.
“We will chase them. God willing, we will complete this operation very quickly.”
Turkey warned the U.S. last week that it would take action in the Afrin district if the U.S. continued to aid Kurdish fighters in the area.
“We emphasized that such a step was very wrong,” Turkey's Deputy Prime Minister Bekir Bozdağ said, according to Reuters.
“Turkey has reached the limits of its patience. Nobody should expect Turkey to show more patience," he continued.
Secretary of State Rex Tillerson said action in the area had been misinterpreted and the U.S. is only looking ”to ensure that local elements are providing security to liberated areas.”