BOGOTA -- Soldiers seized nearly half a ton of explosives and dozens of landmines from a Revolutionary Armed Forces of Colombia, or FARC, factory, but no one was arrested, the army said Sunday.

The factory was found Saturday by counterinsurgency troops in La Holanda, a hamlet in northeastern Colombia, the army brigade based in the city of Arauca, the capital of the like-named province, said.

The facility contained 124 "improvised explosive devices," 450 kilos (991 pounds) of explosives and 150 kilos (330 pounds) of shrapnel, the army said.

Soldiers also seized 470 electronic initiators, 1,200 meters (1,313 yards) of detonating cord and six radios.

The site was "a factory used by FARC terrorists to manufacture antipersonnel mines," the army said.

Landmines have been planted in 31 of Colombia's 32 provinces, according to the United Nations.

Up to 100,000 of the weapons are estimated to have been planted around the Andean nation, the great majority of them by leftist rebels seeking to inflict casualties on soldiers and protect coca plantations that supply their extensive drug trafficking operations.

Almost all of the weapons are "non-industrial" homemade mines manufactured in guerrilla camps at low cost.

Having ratified in 2001 the Ottawa Convention, which outlaws the use, production, stockpiling and transfer of antipersonnel mines, the Colombian government subsequently developed an action plan to rid the country of the buried weapons.

Colombia's first reported incident in which a landmine killed or injured a non-combatant was in 1990, and, since then, hundreds of municipalities have in one way or another been affected by the buried explosives.

Landmine Monitor, a non-governmental organization, said that while some manufactured devices have been imported into Colombia, most of the mines deployed in the Andean nation were more-difficult-to-detect homemade bombs.

The global watchdog organization also noted that 97 percent of Colombia's landmine blasts occurred in rural areas, which together constitute the main battleground in the country's internal conflict.

Colombia is thought to have anywhere from 70,000 to 100,000 landmines buried in its soil, each with a "useful" life of 50 years or so.

The Colombian armed forces destroyed the last 6,814 mines in their arsenals on Oct. 24, 2004.

Landmine Monitor said that planting each mine costs the insurgents less than $2, while it costs the country about $1,000 to eliminate one.

The FARC, Colombia's oldest and largest leftist guerrilla group, was founded in 1964, has an estimated 8,000 to 17,000 fighters and operates across a large swath of this Andean nation.

President Alvaro Uribe's administration has made fighting the FARC a top priority and has obtained billions in U.S. aid for counterinsurgency operations.

A succession of governments have battled Colombia's leftist insurgent groups since the mid-1960s.

The FARC is on both the U.S. and EU lists of terrorist groups. Drug trafficking, extortion and kidnapping-for-ransom are the FARC's main means of financing its operations.