The international decommissioning body has declined to back assertions by Mr Ahern in the Dáil and Mr Blair in the House of Commons that they have been given important extra information that would satisfy unionist demands on weapons destruction if it were made public.
As Mr Blair faced Conservative and DUP allegations yesterday of misleading the House of Commons, a spokesman for Gen de Chastelain refused to confirm or deny the two premiers' statements.
The spokesman told The Irish Times last night that the General, accompanied by Mr Andrew Sens, did not hand over any inventory of IRA weapons when he met the two leaders at Hillsborough last Tuesday.
"We cannot go beyond that," the spokesman added.
Mr Ahern and Mr Blair indicated to their respective parliaments that they have significant extra information concerning the weapons which were decommissioned by the IRA this week, and suggested that their efforts in the days since the Hillsborough debacle have been geared towards making this information public, in order to satisfy Mr David Trimble's demand for "transparent" decommissioning.
However the DUP has asserted - and the decommissioning commission has not denied - that the General told them he gave the premiers no extra information.
On Wednesday, Mr Ahern gave the clear impression that he was in possession of significant extra information, saying he and Mr Blair had considered the argument that the governments should "publish what they know".
He said: "This is something to which the British Prime Minister and I gave some thought yesterday and discussed at length." However "if we were to give the full extent of what he told us yesterday, and he did not tell us everything, that would end that process". He added: "I do not rule out the possibility of saying more about what we were told yesterday." Mr Blair told the House of Commons the same day: "He [Gen de Chastelain] gives certain information - not the full information, but certain information - to us, as the two Governments. Although we are not at liberty to disclose that information without his permission, we are working hard to try to find a way in which we can do so, because I believe, on the basis of what we know, that people would be satisfied if they knew the full details. If people knew the information we know, they would be satisfied."
Dr Paisley yesterday insisted that "as a result of our party's meeting with Gen de Chastelain [on Thursday], we now know that the IICD gave the Prime Minister no more information than he gave the public in his report on Tuesday."
A Government spokeswoman said last night that she could not expand on what the Taoiseach had said, as divulging any information "may cause problems in the future of the decommissioning process".
Asked directly if the General had given the two leaders specific extra information, she repeated that she could not expand on what the Taoiseach had already said.
Mr Blair's official spokesman told The Irish Times last night that Downing Street had to respect the confidentiality of the contacts between Gen de Chastelain and the IRA, and between the General and the Prime Minister. Consequently, he did not want to comment further.