Iraqi and Kurdish forces are exchanging fire at the border between federal and Kurdish lands, days after Kurds withdrew from disputed territories across northern Iraq.

Iraqi artillery forces shelled Kurdish military positions north and south of the town of Altun Kupri. Thick smoke could be seen rising from a checkpoint just north of the town.

Kurdish forces responded with rocket fire.

Kurdish authorities have sent reinforcements to the front lines. An Associated Press team saw a convoy of 50 armored vehicles arriving at the Kurdish side of the front.

The U.S. is seeking to stay neutral in a conflict between two allies against the Islamic State, prompting concerns whether the distraction could derail the efforts to stabilize the region.

U.S. State Department spokesperson Heather Nauert earlier this week said the U.S. is urging all sides to “restore calm” to “avoid further clashes.”

Iraq's federal authority claims Altun Kupri for itself as it is part of the areas acquired by the Kurds in 2014, when Iraqi soldiers gave up their posts in the face of an Islamic State group advance.

The Associated Press contributed to this report