The rebel safe haven was supposed be a "laboratory for peace," but Colombian officials say members of the Irish Republican Army were training Colombian rebels in terrorist tactics there.

The accusations, leveled Monday following the arrests of three alleged IRA members in Bogota, prompted fears of a turn to urban terrorism by Colombia's largest insurgency, the leftist Revolutionary Armed Forces of Colombia, or FARC.

They were also bound to stir up further criticim of President Andres Pastrana's decision to cede 16,200 square miles of Colombian territory as a peace gesture to the rebels.

Announcing the arrests at a news conference, Defense Minister Gustavo Bell said three men were caught Saturday after spending five weeks inside the FARC-held demilitarized zone training rebels in the use of explosives.

In return, officials said the FARC could be providing the IRA with anything from drugs to money to black market arms — their first such alliance.

Officials said tests on the clothing of the three turned up traces of four different kinds of explosives, as well as cocaine and amphetamines. FARC rebels are involved in cocaine production in Colombia, which earns them millions of dollars in profits.

The 16,000-strong rebel army has mostly used crude explosive devices in Colombia's civil war, now in its 37th year.

Mora said British officials have confirmed that the three suspects were members of an IRA unit that specializes in explosives and arms manufacturing.

The arrest of the three may also have worked to undermine efforts to salvage the Catholic-Protestant government at the heart of Northern Ireland's 1998 peace accord. Protestants said the arrests showed that the IRA was not ready to renounce violence, a key principle underpinning the whole peace process.

According to Jeffrey Donaldson, a senior leader of the Ulster Unionist Party, the arrests in part indicates "that the IRA is as wedded as ever to the theology of revolutionary terrorism."

The three residents of Northern Ireland entered Colombia with false passports at the end of June and the beginning of July, the officials said. Two of the men have been identified as Martin McCauley and James Monaghan.

The third member of the group, considered the most high-ranking of the three, has still not been identified. He traveled under the name David Bracken, believed to be a pseudonym, and is said to be the only one who speaks Spanish.

An official from Colombia's federal prosecutor's office said the three could also be tried here for providing training in terrorist tactics, and could receive jail terms of up to 20 years if convicted.

The three were captured after getting off a flight at Bogota's international airport from San Vicente del Caguan, the largest town in the demilitarized zone. They had intended to board a plane bound for Paris.

Rebel spokesman Raul Reyes, reached by the phone from the DMZ, refused to comment on the arrests. There was no immediate comment from the IRA, either.

The FARC, with its huge earnings from cocaine production and kidnappings, is considered a largely self-sufficient group. However, armed forces chief Gen. Fernando Tapias said the military had received past reports of training from Venezuelan and Cuban "terrorists", and had noted growing coincidences between terror tactics used by Colombian rebels, the IRA and Spain's armed Basque group ETA.

"Every war is going to get resources from outside elements," Tom Cash of Kroll Associates, a New York-based security consultant firm said from his Miami office. "The IRA is global in its arms and explosives networks, and I don't see why anyone would be surprised to see that they are assisting the FARC."