The political crisis in Northern Ireland worsened last night as the IRA warned the governments in London and Dublin: "Do not underestimate the seriousness of the situation."

The Guardian reports that 24 hours after the Provisional IRA withdrew its long awaited promise to decommission its weapons, London and Dublin are convinced the IRA and its political wing, Sinn Fein, are bluffing, and also insist that the IRA's ceasefire will hold.

Meanwhile sources in Washington confirmed that the Bush administration is considering excluding Sinn Fein's president, Gerry Adams, from the annual St Patrick's Day celebrations at the White House on March 17. 

Last night the two governments insisted the focus must be maintained on the issue of paramilitary "criminality", but Sinn Fein again denied the  charge of being involved in last December's Belfast bank robbery, and the IRA seemed to hint at an end to the ceasefire.

In a  statement, a senior republican source said: "The two governments are trying to play down the importance of our statement because they are making a mess of the peace process. Do not underestimate the seriousness of the situation."

That statement echoed comments by Adams yesterday that the peace process could be "as transient as Tony Blair's time in Downing Street."