Turkish artillery explodes near US special forces in northern Syria No U.S. troops were killed or injured in the explosion.

U.S. special forces operating in northern Syria have been moved from their location after Turkish artillery exploded near their outpost, according to a U.S. official.

Two other U.S. officials said the explosion occurred Friday afternoon, Eastern Daylight Time, in the vicinity of U.S. special forces operating near the Syrian city of Kobane, just across the border from Turkey. No U.S. forces were killed or injured.

The explosion was not a "direct hit" on U.S. forces, one official said, and it does not appear to have been deliberate.

In a statement, Turkey's defense ministry said the strike was in response to mortars coming from "terrorists" operating near the U.S. special forces outpost. The statement said that Turkey was not targeting the U.S. troops and that precautions were taken to prevent damage to the U.S. fortification.

The artillery fires landed on the third day of a Turkish military operation targeting America's Kurdish allies in northern Syria, who are credited with defeating the Islamic State. It represents a nightmare scenario for defense officials who have repeatedly expressed concerns about the security of U.S. forces operating inside Syria after the Turkish incursion.

During a Pentagon briefing on Friday, Chairman of the Joint Chiefs of Staff Gen. Mark Milley told reporters that Turkey knew the locations of U.S. forces in Syria.

"The Turkish military is fully aware, down to explicit grid-coordinate detail, of the locations of U.S. forces," Milley said. "Everyone if fully aware we are the United States military. We retain the right of self-defense."

Earlier this week, the U.S. pulled about 50 American troops away from two observation posts along the Turkey-Syria border in advance of the Turkish military operation, citing force-protection concerns. Those troops were moved to another location in northern Syria. Officials told ABC News that there are plans to withdraw all U.S. troops from Syria if the security situation worsens.