By Idrees Ali and Phil Stewart
WASHINGTON (Reuters) - An explosion that may have been caused by Turkish artillery struck near a U.S. military outpost in northern Syria on Friday, but no U.S. personnel were reported hurt, U.S. officials said, an incident that highlights the risks to U.S. troops as Turkey wages an offensive in the region.
Turkey's Defense Ministry said it had taken all measures to ensure that no U.S. base was damaged while it responded to harassment fire that originated near a U.S. base near Kobane in Syria.
"The firing was ceased as a result of the issue being relayed to us by the U.S.," the defense ministry said in a statement.
The U.S. officials, speaking on the condition of anonymity, said the source of the explosion was unclear. It coincided with an offensive by Turkey in northeast Syria against U.S.-allied Kurds.
The officials said U.S. troops were in the outpost at the time, but there had been no further activity since. U.S. forces have had a successful partnership with Kurdish YPG militia in Syria to oust the Islamic State group.
One of the U.S. officials said the explosion occurred several hundred meters from the base where U.S. special forces were located and the initial belief is that Turkey was responsible because Turkish artillery was pointed in the general direction of the U.S. outpost.
Turkey's Defense Ministry said there was no firing on the U.S. observation post.
"There was no firing on the U.S. observation post," it said, adding that it fired in response to an attack on its military posts south of the town of Suruc, across the border from Kobane.
The Chairman of the Joint Chiefs of Staff General Mark Milley told reporters at the Pentagon earlier on Friday that Turkey had been told of U.S. positions in Syria, "down to explicit grid coordinate detail."
Top Pentagon officials stressed the need for Turkey to avoid doing anything to endanger U.S. forces inside Syria, which numbered about 1,000 before the incursion. Although U.S. troops had no intention of firing on Turkey, a NATO ally, the Pentagon noted they had the right to defend themselves.
"Everyone is fully aware that we are the United States military. We retain the right of self-defense," Milley said.