America last night warned that Sinn Fein is under increasing pressure after it confirmed that provisional IRA members had been involved in terrorist activities in Colombia.

Richard Haass, the most senior US diplomat working on Northern Ireland, said the three suspected IRA members who were arrested in Bogota last month and are currently residing in a Colombian jail "were not there for vacationing".

He went on to claim that the IRA trio were involved in discussions about matters which can only be associated with activities that would fall under the rubric of terrorism".

In addition to warning Gerry Adams that "this must never happen again", Haass also raised his concerns over the IRA's reluctance to decommission its weapons. He said that the refusal to put its weapons verifiably beyond use "is a characteristic of a paramilitary operation".