WASHINGTON - An unseemly incident during Turkish President Recep Tayyip Erdogan's recent visit to Washington is adding to U.S.-Turkish tensions.

The U.S. says it summoned Turkey's ambassador to the State Department to raise concerns about Erdogan's security detail, seen on video violently breaking up a protest earlier this week outside the Turkish ambassador's residence.

Still, the Trump administration is facing growing calls to respond even more forcefully. The U.S. concedes that it released two Turkish presidential guards after holding them briefly after the incident. They were released under a globally recognized custom under which nations don't arrest members of a visiting president's delegation.

The tensions between the allies are also compounded by a growing spat over U.S. support for Kurdish fighters in Syria. Turkey considers them to be terrorists who threaten Turkey.