The United States is concerned about Turkey’s announced offensive against Kurds in northern Syria. This could endanger US troops stationed there and destabilize the region, the US government warned on Thursday.

“We have spoken to the Turkish government and opposed military action on the Syrian side of the border,” said US Ambassador to the United Nations Linda Thomas Greenfield in the Turkish city of Hatay near the Syrian border. Nothing should be done to break the truce.

The US-backed Syrian Democratic Forces (SDF), which includes Kurdish forces, warned an offensive could trigger a humanitarian crisis. In addition, the fight against the extremist group Islamic State could be endangered.

Turkey’s goal is to create a 30-kilometer-wide security zone along Turkey’s southern border, Erdogan announced on Wednesday. In the past few days, violence in the border area has increased, informants on both sides of the Reuters news agency said. However, no major military movements were noticed.