Political talks planned for London next week involving all the Northern Ireland parties have been postponed.
Mr Blair and Mr Ahern had been due to host the talks
Government sources told the BBC on Monday that they still hoped to hold the discussions before the European elections in June.
They added that more work was required before the discussions, aimed at moving the political process forward, were called.
It had been planned that three days of proximity talks involving Northern Ireland's politicians would be hosted by the British and Irish prime ministers.
The discussions were due to follow the publication on Tuesday of the Independent Monitoring Commission's first report on continuing paramilitary activity.
Sinn Fein President Gerry Adams described the cancellation as an example of the "ad hoc and almost casual attitude of London and Dublin towards the process".
Such behaviour was "unacceptable", he said.
"It follows on from the Irish government's decision to run with a referendum
on citizenship and the expected IMC Report. Both are in
contravention of the Good Friday Agreement."
Gerry Adams said the governments' behaviour was "unacceptable"
On Tuesday, Ulster Unionist negotiator Sir Reg Empey said he was not surprised that the talks had been postponed.
"I could not see precisely what the prime minister was hoping to achieve when there is no sign of a breakthrough and why, against the background he has in Iraq and other places, he wanted to set himself up for another failure," he said.
The latest deadlock in the political process follows claims of IRA involvement in the alleged false imprisonment of a dissident republican in Belfast in February.
The assertion by Chief Constable Hugh Orde that Provisional IRA members were behind it have overshadowed the review of the Good Friday Agreement, with UUP leader David Trimble walking out of the talks.
Following last November's assembly election, the Democratic Unionist Party overtook the UUP as the main unionist party in Northern Ireland.
With the DUP refusing to negotiate with Sinn Fein and the Ulster Unionists not participating in the review, no round table sessions are being held.
The political institutions in Northern Ireland were suspended in October 2002 amid allegations of IRA intelligence-gathering in the Northern Ireland Office.