The Pentagon has said that US troops in Syria came under artillery fire from Turkish forces on Friday, in an area where Turkey knows Americans are present.
Navy Capt. Brook DeWalt, a Pentagon spokesman, said the artillery explosion came within a few hundred meters of the area where US troops were.
He added that no troops were injured and US forces have not withdrawn from the town of Kobane.
Turkey said the US was not the target.
DeWalt warned that Turkey must avoid actions that could result in immediate defensive action by the US.
This is the first time a coalition base has been in the line of fire since Turkey's offensive on Kurdish forces in northeast Syria began Wednesday.
US officials said a number of US troops left their post on a hill outside Kobane after coming under fire. The officials said a large base in the town has not been affected by the shelling.
They expected the evacuation to be temporary.