DUP leader Peter Robinson has described the UUP’s decision to quit the power-sharing executive over the Provisional IRA as “illogical”.
The First Minister also accused the UUP of running away from the political battlefield by leaving the five-party devolved coalition.
However, UUP leader Mike Nesbitt hit back at Mr Robinson.
In a tweet this morning, Mr Nesbitt said: “There is no battlefield. The DUP promised a battle but only bluster.”
In his first major response to the crisis threatening devolution, Peter Robinson said it was “a time for cool heads, clear thinking and a steely resolve to ensure that democracy and the rule of law triumph over terror and murder”.
The UUP moved from government into opposition after its ruling executive met on Saturday.
The party made the decision after police chiefs said the Provos were involved in the murder of Kevin McGuigan.
However, the two unionist parties differ on how to respond to the McGuigan murder. Sinn Féin meanwhile have accused the UUP of simply scoring political points against its bigger unionist rival by exploiting the McGuigan killing.
Writing in today’s Belfast Telegraph, Mr Robinson confirmed the DUP would be meeting Prime Minister David Cameron on Tuesday to discuss the crisis.
“In the coming days, we will hold fast to the fundamental principle that those who are in government in Northern Ireland cannot also be involved with those who engage in paramilitary and criminal activity,” the DUP leader wrote.
Criticising the UUP as irresponsible, Robinson said: “Exiting the field of play is not a tactically clever first option – it can only ever be a last resort.”
He added: “This is not the time to flee the battlefield, it is the time to confront violent republicanism, to stand and fight for democratic principles and to do what is right for the law-abiding citizens of Northern Ireland who want to see our country prosper and reach its full potential.”.
The DUP is more likely to try to have Sinn Féin suspended from the executive – a move that is unlikely to the win the backing of the remaining two parties in the coalition, the nationalist SDLP or the Alliance party.
If moves to suspend or expel Sinn Féin fail then there will be calls within the DUP to follow the UUP out of the executive, triggering its collapse.