BEIRUT — A U.S. envoy doubled down on Washington’s support for Syria’s new government, saying Monday there is “no Plan B” to working with it to unite the country still reeling from years of civil war and wracked by new sectarian violence.

Hundreds of people have been killed in days of violence in southern Syria which began with clashes between members of the Druze minority group and Bedouin tribes and drew a military intervention from Syria.