The Colombian military killed at least seven leftist militants during an assault on a rebel base, Defense Minister Juan Carlos Pinzon said.

Pinzon said the dead included a woman who was a regional commander of the National Liberation Army (ELN), the second largest left-wing guerrilla group after the FARC, which has been at war with the Colombian government for decades.

"At this point we know that seven members of the organization have fallen and that another four members have been wounded or captured," he told reporters during a visit to a military base in the country's southeast.

The attack took place in the northwest Antioquia department.

One of the bodies was identified as Maria Orlinda Guerrero, whom Pinzon said was "one of the most violent people" in the ELN and the mastermind of the hijacking of a commercial airliner in 1999.

The group landed the plane and kidnapped around 40 passengers, marching them off into the jungle.

Today the Cuba-inspired ELN counts some 2,500 members, while the better-known Revolutionary Armed Forces of Colombia (FARC) -- Latin America's longest-fighting insurgency -- numbers some 8,000.

Navy Admiral Roberto Garcia, meanwhile, said Ecuadoran authorities arrested five FARC rebels with explosives, along the countries' shared border.

"This is an example of how, working together, in this case with Ecuador, we can fight the FARC more effectively," President Juan Manuel Santos said at the base. The government invited reporters to the southeastern base to highlight a campaign to encourage both the FARC and ELN to lay down arms to honor the Christmas holiday.