Sinn Fein has dismissed Ian Paisley's claim that the IRA is considering destroying its weapons without photographic evidence.
DUP leader Ian Paisley met Paul Murphy and Dermot Ahern
Mr Paisley made the remarks after the DUP and other parties held talks with British and Irish officials.
Sinn Fein's Mitchel McLaughlin said his comments were "the stuff of Alice in Wonderland".
Tony Blair and Bertie Ahern meet on Thursday to consider ways of breaking the deadlock over guns and photos.
Mr Paisley warned an IRA arms move without photographic evidence would have "very serious consequences" for the political process.
Speaking after meeting Northern Ireland Secretary Paul Murphy and Irish Foreign Minister Dermot Ahern, he said negotiations had been "in the context of complete verifiable and transparent decommissioning".
Three previous republican arms moves have been witnessed by members of the Independent International Commission on Decommissioning (IICD).
Mr Paisley said: "There is an indication that the IRA may be considering proceeding to decommission its weapons under the original IICD scheme, leaving out the additional elements relating to transparency included in the draft statement from the IICD which formed part of our comprehensive agreement.
"We want to make it clear that if the IRA does not fulfil its obligations as envisaged in the comprehensive agreement, then its refusal to meet these terms would have very serious consequences in respect of the DUP's attitude to other elements of the comprehensive agreement."
However, Mr McLaughlin said Mr Paisley "giving an ultimatum to the IRA not to deal conclusively with its weapons" was "an absurd situation which would be laughable if it were not so serious".
After the meeting with the DUP, Mr Murphy said both governments would welcome decommissioning, but it would have to be done in such a way that it would bring confidence in the community.
He added that any arms move in itself would not produce a "political settlement, however good decommissioning would be".
Asked about Mr Paisley's claims that the IRA planned to press ahead with decommissioning, he said: "I have no information to that effect."
Proposals published jointly by the two governments last week included a plan for the IRA to allow photographs to be taken of its weapons being put beyond use in the presence of independent witnesses.
The DUP argued that this was necessary to ensure that there was confidence in the act of decommissioning.
But Sinn Fein said the IRA would "not submit to a process of humiliation".
The political institutions in Northern Ireland have been suspended since October 2002 amid allegations of IRA intelligence gathering at the Northern Ireland Office.
The DUP and Sinn Fein became the largest unionist and nationalist parties after assembly elections in November 2003.
However, the two parties have not been able to reach a deal which would allow a power-sharing executive to be formed, and Northern Ireland continues to be governed by direct rule from Westminster.