A day after President Donald Trump announced he would withdraw U.S. troops from northeastern Syria, Turkey on Tuesday said it is moving ahead with military operations in the country targeting Kurdish forces.

“All preparations for the operation have been completed,” Turkey’s defense ministry said.

The Syrian Democratic Forces (SDF) reported on Twitter that Turkey had begun shelling an SDF post in a border city, but said none of its forces were injured and that it had not responded to “this unprovoked attack.”

Late on Monday, the U.K.-based Syrian Observatory for Human Rights countered reports that bombing by Turkish forces had already begun that day.

Reports that Turkish troops and tanks were assuming positions along the Turkey-Syria border was causing tension in the border city of Akcakale Tuesday, according to Al Jazeera.

“There’s a lot of tension here,” said Al Jazeera reporter Charles Stratford. “There are huge concerns about the security ramifications this operation could have. It’s very difficult to predict when any military operation might start.”

The SDF, which includes many Kurdish fighters and which spent years helping the U.S. to combat ISIS in the region, said troops were standing ready to fight a possible Turkish attack—without the help of the United States.