Five people died and one was wounded when gunmen attacked a bar in Tumaco, a port city in southwestern Colombia, city officials said Sunday.
Investigators are trying to determine whether the victims belonged to a criminal organization, Tumaco Mayor Victor Gallo told reporters.
"There are indications that these people belonged to the group of the Los Rastrojos gang," Gallo said.
The victims were talking early Sunday when "several armed people opened fire on them indiscriminately," the mayor said.
The massacre occurred in Bucheli, which is located outside Tumaco, a Pacific port city in Nariño province.
Drug traffickers and Revolutionary Armed Forces of Colombia, or FARC, guerrillas operate in the area.
Los Rastrojos is one of a number of gangs founded by veterans of the defunct United Self-Defense Forces of Colombia, or AUC, militia federation.
Los Rastrojos and the other AUC successor groups, such as Los Paisas and Nueva Generacion, are responsible for a good deal of the criminal activity in Colombia, officials say.
Venezuelan authorities arrested Diego Perez Henao, known as "Diego Rastrojo" and considered the gang's top boss, in June.
Perez Henao, who was the target of an intense manhunt by U.S. and Colombian authorities, was hiding out at a ranch in Venezuela's Barinas state.
The Los Rastrojos boss was the subject of a nearly $6 million reward.
The AUC, accused of committing numerous human rights violations, demobilized more than 31,000 of its fighters between the end of 2003 and mid-2006 as part of the peace process with former President Alvaro Uribe's administration.
The group was made up of numerous rural defense cooperatives formed more than 20 years ago to battle leftist rebels.
Many of the militias, however, degenerated into death squads and carried out massacres of peasants suspected of having rebel sympathies, along with slayings of journalists and union members accused of favoring the leftist insurgents.
On May 13, 2008, the Colombian government extradited 14 former AUC chiefs to the United States.
The former AUC commanders were wanted in the United States on drug, money laundering and other charges. EFE