Some buses in the capital of El Salvador have stopped running after two drivers were killed and rumors circulated that the Central American country's "Mara" street gangs planned to burn buses.

Authorities in San Salvador added supplementary service using government-owned buses Monday after some lines stopped running. Transport Vice Minister Nelson Garcia said only a small percentage of the nation's bus service was affected.

The street gangs have targeted bus drivers in the past with extortion demands, requiring them to pay protection money to operate or risk having their buses burned or being killed.

The attorney general's office reported two drivers were killed Monday morning.

Assistant national police director Howard Cotto said gang members had distributed leaflets at bus terminals with threats against bus owners.