The public spat between the White House and the US commission probing the 11 September attacks has escalated over the Bush administration's claims.
The 9/11 commission released a statement on Tuesday saying it was aware of no new information proving the existence of cooperative pre-war ties between Iraq and al-Qaida, despite the administration's claims to the contrary.
The brief statement came in response to comments by Vice-President Richard Cheney, who suggested the 9/11 commission might have not had access to all available information on the subject.
But the panel made up of 10 prominent Americans representing both major political parties disagreed.
"After examining available transcripts of the vice-president's public remarks, the 9/11 commission believes it has access to the same information the vice-president has seen regarding contacts between al-Qaida and Iraq prior to the 9/11 attacks," the statement said.
The terse response was the latest round in a series of testy exchanges triggered by the commission's finding that the ousted Iraqi government of Saddam Hussein and Usama bin Ladin's al-Qaida network had no "cooperative relationship".
Dick Cheney maintains al-Qaida
and Saddam were linked
The finding, made public last month, disproved a key argument used by the administration of President George Bush to justify its March 2003 invasion of Iraq.
The Bush administration insisted in the lead-up to the war that al-Qaida and Saddam Hussein's government had developed a "sinister nexus" that might result in terrorists gaining access to weapons of mass destruction.
But in a report released on 16 June, the commission said al-Qaida leader bin Ladin was actively opposed to Iraq's secular government and at one time even sponsored an anti-Saddam Islamist group based in Iraqi Kurdistan.
Later, authorities in Sudan, where bin Ladin had found refuge in the early 90s, reportedly persuaded the al-Qaida chief to drop that support and attempt to make amends with Baghdad, according to the document.
As part of these efforts, a senior Iraqi intelligence officer reportedly made three visits to Sudan and finally met bin Ladin in 1994, the report said.
But nothing appears to have come out of this courtship, according to the commission.
Bin Ladin is said to have requested space for establishing al-Qaida training camps in Iraq as well as assistance in arming the groups, "but Iraq apparently never responded," said the commission.