Colombian authorities say at least seven people were killed and 68 others injured when a bomb exploded Wednesday at a shopping center in the northeastern city of Cucuta.
The blast ripped through an underground parking lot, igniting parked cars and causing an avalanche of concrete as panicked shoppers tried to escape.
Family members of shopping center employees gathered nearby, awaiting word on the fate of their loved ones.
Authorities say leftist rebels of the National Liberation Army, the ELN, are to blame for the blast. Police offered no evidence and the guerrillas did not claim responsibility.
The ELN, as well as the nation's largest rebel group, the Revolutionary Armed Forces of Colombia, FARC, are fighting outlawed rightist paramilitary groups for control of Cucuta.
The latest incident occurred as U.S. Under Secretary of State Marc Grossman met with Colombian President Alvaro Uribe at the presidential palace in Bogota.
The talks also followed the crash three weeks ago of a U.S. government plane in rebel territory in southern Colombia.
Three Americans were kidnapped by the FARC. A fourth American and a Colombian soldier were found shot to death at the crash site. The United States brands Colombia's outlawed groups as terrorists.
In recent years, the United States has provided Colombia with an estimated $2 billion in mainly military aid for counternarcotics efforts. Washington has now expanded that assistance to counter-insurgency operations.
Colombia has been torn by a 39-year civil war that pits the rebels, paramilitaries and the government against each other. Some 3,500 people, mainly civilians, are killed in the fighting each year.