WASHINGTON/BEIRUT, May 18 (Reuters) - The U.S. military carried out an air strike on Thursday against militia supported by the Syrian government that posed a threat to U.S.-backed fighters in the country’s south, U.S. officials told Reuters on Thursday.

One of the U.S. officials said the strikes near the town of At Tanf destroyed at least one tank and a bulldozer, and another said it followed warning shots by U.S. aircraft meant to dissuade the fighters from advancing further.

A member of the U.S.-backed Syrian rebel forces told Reuters the strikes hit a convoy of Syrian and Iranian-backed militias that were heading toward a base used by U.S. and U.S.-supported forces.

Muzahem al Saloum, from the Maghawir al Thwra group, told Reuters that the jets struck after some rebel forces clashed with Syrian and Iranian militias after they had advanced to about 17 miles (27 km) from the base.

“We notified the coalition that we were being attacked by the Syrian army and Iranians in this point, and the coalition came and destroyed the advancing convoy,” Saloum said.

The Pentagon did not immediately respond to requests for comment.

Since they appeared defensive in nature, Thursday’s strikes did not suggest a shift in the U.S. military’s focus in Syria, which has been on battling Islamic State militants.

Still, the strikes would be the first against fighters aligned with Syria’s government since the United States waged cruise missile strikes on a Syrian air base in April.

The April strikes were ordered in retaliation for a chemical weapons attack that Washington blamed on Damascus, and were described as a one-off measure to deter any future chemical weapons use.