Online videos show Syrian rebels using what appear to be U.S. anti-tank rockets, weapons experts say, the first significant American-built armaments in the country’s civil war.

They would signal a further internationalization of the conflict, with new rockets suspected from Russia and drones from Iran also spotted in the forces of President Bashar al-Assad.

None of that equipment, however, is seen as enough to turn the tide of battle in a now broadly stalemated war, with Assad dominant in Syria’s central cities and along the Mediterranean coast and the rebels in the interior north and east. […]