Local civil protection officials say eight Americans are among the dead and the U.S. Embassy has confirmed the identities of four, said Embassy spokeswoman Liz Detter. The Embassy could not release their names because next of kin had not been notified.
"Our heartfelt condolences go out to all those killed and injured in this tragedy," Detter said.
Canadian foreign affairs spokesman Alain Cacchione said Canadians were involved in Monday's accident but he declined to provide further details for privacy reasons.
Coahuila state police commander Armando Santana said 11 people were killed in the crash and 15 were injured.
He said the bus was carrying a group of Texas retirees from McAllen, Texas, to the northern Mexican state of Zacatecas. Detter said 19 Americans were on board.
The truck driver apparently lost control and swerved into the bus's lane on a highway outside the city of Saltillo, Santana said. He said the bus driver was killed and the truck driver was among the injured.