A huge explosion in the South Armagh border area killed two Irish Republican Army guerrillas Monday in ``an unfortunate accident,'' the IRA said. The blast destroyed a van and a barn about two miles outside Crossmaglen village, badly damaged two cars and left a crater. Police said four armed and masked men hijacked the van and a car shortly before the blast. Authorities speculated that IRA guerrillas were installing explosives in the van when the explosives accidentally detonated. A police officer, speaking anonymously in keeping with British practice, said it was believed the IRA's intended target was an army observation post near the border with Irish Republic. The IRA later issued a statement saying two of its men died in the blast, which it described as ``an unfortunate accident.'' The group gave no details, and said names and IRA ranks of the dead men would be released after families are notified. Police said human remains were found at the site and walkie-talkies and a notebook were among the debris. Helicopters brought security forces into the surrounding fields to seal off the area overnight. Police said they would not move in until Tuesday, after army bomb disposal experts made sure no booby-trap bombs were around. The mostly Roman Catholic IRA often uses explosives in its violent campaign to drive the British out of the predominantly Protestant province and unite it with the overwhelmingly Catholic Irish Republic.