The British government will "certainly" take action to ensure Sinn Fein's expulsion from the talks process if the party does not honour its commitment to the Mitchell Principles.
And in a clear signal that Mr Tony Blair will hold Sinn Fein to the principles with "total determination", government sources said yesterday Mr Gerry Adams would be asked to explain the An Phoblacht/Republican News article when the talks resume on Monday.
In spite of the hopes raised by Sinn Fein's pledge on Tuesday, yesterday's IRA comment that it "would have problems with sections of the Mitchell Principles" could not have come at a more sensitive stage.
The Ulster Unionist Party executive committee meets tomorrow to decide if the party will attend the talks. But the crucial question facing the party, should it agree to join, is that it must then decide in what form it will participate. UUP sources indicated earlier this week the executive committee would recommend "proximity talks" on a "time-limited" basis.
The UUP leader, Mr David Trimble, said on BBC television's six o'clock News: "It shows how thoroughly dishonest an exercise this is, with people whom we know are leading members of the IRA turning up to endorse the Mitchell Principles last Tuesday and then attempting to wriggle out from underneath them today. It won't wash."
The British government is understood to be "very, very concerned" by the IRA's comments.
Asked if the statement altered in any way Sinn Fein's participation in the talks, a Northern Ireland Office spokesman said: "If they [Sinn Fein] do not stand by the Mitchell Principles, we will certainly take action. They will be out of the negotiating process. It is pretty bad timing, or good timing, depending on which way you look at it. It's certainly not making things easier for Mr Trimble."
London is also pointing to the commitment in the principles whereby participants agree to "renounce for itself, and to oppose any effort by others, to use force, or threaten to use force" to influence the outcome of the talks.