Fifteen Colombian soldiers have been killed in an ambush by leftist FARC fighters, the country's president said, raising concerns about peace talks launched last year.

The soldiers were killed in the ambush on Saturday in Arauca on the border with Venezuela, AFP reported.

"Our hearts are with the families of the fifteen heroes who sacrificed their lives in Arauca for the tranquillity and security of their fellow citizens," President Juan Manuel Santos said on Sunday.

The soldiers were killed in the ambush on Saturday, AFP reported.

Meanwhile, an explosive detonated in a nightclub in northeastern Colombia early on Sunday, killed at least one person and injured 20, authorities said.

"We are trying to establish whether it was the act of criminal gangs," police chief Carlos Rodriguez told reporters in the border city of Cucuta where the incident occurred.

An unidentified person detonated what was probably a grenade, police said.

Most of the victims were injured by shrapnel, according to Rodriguez.

Source: Agencies