Colombia's FARC rebels have executed four hostages, just days after installing a new leader at the helm of Latin America's longest-running insurgent group, the defense minister said Saturday.

"Four hostages, members of the security forces, have been killed," Defense Minister Juan Carlos Pinzon told a press conference, adding that their bullet-ridden bodies had been found on Saturday morning in the Solano region.

The Southeast Asian Games officially open on Friday in Indonesia, where beleaguered organizers have admitted to battling a slew of problems including corruption, unfinished venues and poor ticket sales.

Eleven nations will contest sports from athletics and swimming to sepak takraw -- a cross between football and volleyball -- in the biennial Games held in the Indonesian capital Jakarta and Palembang in South Sumatra.

The top leader of Colombia's main rebel group, the bookish ideologue Alfonso Cano, was killed Friday in a military raid in the country's southwest, authorities said.

The death was a major victory for President Juan Manuel Santos, coming just over a year after the military killed the rebels' field marshal. It was anything but a fatal blow, however, to the nearly half-century-old peasant-based insurgency.

Police have raided and destroyed a huge drug processing lab in eastern Colombia, seizing six tons of cocaine with a street value of $180 million, the force's chief narcotics officer said Friday.

"Police located and destroyed a cocaine production megalaboratory that belonged to the ERPAC drug gang," General Luis Alberto Perez said.

The U.S. Congress has approved long-stalled free trade agreements with Colombia, Panama and South Korea that President Barack Obama trumpeted as engines of growth and job-creation.

The accords will "significantly boost exports that bear the proud label 'Made in America,' support tens of thousands of good-paying American jobs and protect labor rights, the environment and intellectual property," Obama cheered after the pacts were approved on Wednesday.

Suspected leftist guerrillas have attacked a pipeline in northeastern Colombia, the army said, in the latest assault on the country's vital oil sector.

The attack on Wednesday was believed to have been carried out by the Revolutionary Armed Forces of Colombia (FARC) or the National Liberation Army (ELN), which are active in the area, an army brigade spokesman told Agence France Presse.

Colombia's Supreme Court has upheld a 24-year jail sentence against a drug cartel-linked former justice minister convicted of taking part in the assassination of a rival presidential candidate in 1989.

The decision will send the former minister, Alberto Santofimio, back to prison for the murder of Luis Carlos Galan. Santofimio was first sentenced in 2007 but was released the following year on appeal.

A massive uncut emerald on exhibit in Colombia's capital is being touted by its owners as the biggest in the world, officials said Saturday.

The 11,000-karat raw green gem weighs in at 2.27 kilos (almost five pounds) and is on show in Bogota 12 years after it was mined in Muzo, in the South American nation's emerald country in Boyaca province.

Three Chinese workers for the British oil company Emerald Energy have been taken hostage in southern Colombia, officials said Thursday, blaming the kidnapping on FARC guerillas.

A fourth foreigner, who was working as a translator, was also taken hostage, said Edilberto Ramon Henido, secretary of the local government in southern Caqueta department, but he could not confirm the man's nationality.

An explosion likely caused by a methane gas buildup ripped through an underground coal mine in Colombia during a shift change Wednesday, killing 21 workers, officials said. A similar fatal blast occurred at the same mine four years ago.

Five of the victims died at the mine's entrance and by afternoon two bodies had been removed from the mine with another 14 left to recover, said the provincial Colombian Red Cross director, Johel Enrique Rodriguez.