BOGOTA, Colombia (CNN) --Bogota police and U.S. investigators were looking for clues Sunday to determine who was behind near-simultaneous grenade attacks on two bars in northern Bogota that killed one person and wounded 72 others.

The fatality in Saturday's attacks was a Colombian woman, police said. Police said they believe four to six of the victims are civilians from outside Colombia.

The bars -- the Bogota Beer Company and Palos de Moguer -- are popular among U.S. contractors who are in the city to help Colombia with security and anti-drug efforts.

No one has claimed responsibility, and police said it was too early to determine who may have been behind them, or their motive.

The bars are owned by the same family and are about 20 yards from each other. Police said they have a Colombian man in custody and they believe four other men were also involved in the attack.

U.S. Embassy personnel and agents from the Bureau of Alcohol, Tobacco and Firearms are involved in the investigation. The agents are in Colombia as part of a program to help train Colombian police and military.

Colombia has faced decades of civil warfare, involving government troops, leftist rebels and right-wing paramilitary groups.

The right-wing paramilitary forces have had a traditional presence in Bogota's commercial district for years, blackmailing traders in return for protection.

Leftist rebels have increasingly been bringing the war to the nation's cities. In an October attack in Bogota, a car bomb killed at least six people in the city's commercial district.

In September, an explosion in Florencia killed 10 people and wounded 54 others, police said.

In February, the bombing of a Bogota social club killed 32 people and wounded 200. And in August 2002, a mortar attack on the presidential palace in Bogota killed at least 13.

Police said FARC rebels likely were behind the September and February incidents.

Established in 1964 as the military wing of the Colombian Communist Party, 16,000-member FARC is Colombia's oldest, largest, most capable and best-equipped Marxist rebel group, according to the U.S. Department of State. It is classified by the State Department as a terrorist group that conducts bombings, murders, kidnappings and hijackings.

Journalist Karl Penhaul contributed to this report