The IRA has denied an intelligence assessment it held on to some weapons after its "final act" of decommissioning arms last year.
The IMC report is into paramilitary activity in Northern Ireland
The claims about weapons were made to the Independent Monitoring Commission which published its latest report on paramilitary activity in NI.
The IRA is still gathering intelligence, according to the report.
However, the commission said the IRA seemed to be "moving in the right direction".
The IMC said it received reports that the IRA held on to some of its weapons, possibly for personal protection or area protection.
The head of the body responsible for overseeing decommissioning, General John de Chastelain, said there was no indication that the "quantities of arms involved were substantial".
But one of the IMC's commissioners, Lord Alderdice, said they had received a number of "credible reports" which meant they could not share the general's assessment.
"The level of confidence which he's expressed...is not a level of confidence about full decommissioning that we are in a position to share," said Lord Alderdice."
In a statement on Wednesday, the IRA denied the allegations that the organisation had gone back on its pledges made last year.
A statement signed by the Provisionals' pen name P O'Neill said: "Recent allegations that the IRA is in breach of its public commitments are false.
"The IRA has honoured all public commitments made on July 28, 2005. Any allegations to the contrary are politically motivated."
In Wednesday's report, the IMC said that while some of the intelligence gathering activity may be for defensive purposes, it is primarily for pursuing its political strategy.
It believes the activity has been authorised by the IRA leadership. It is also claimed some IRA members were still involved in organised crime.
General de Chastelain's decommissioning body said it had submitted a report to the British and Irish governments.
It said: "Last week, we were informed by security sources in Northern Ireland that they had intelligence to the effect that some individuals and groups within the IRA have retained arms including handguns.
"There was no indication that the quantities of arms involved were substantial."
Northern Ireland Secretary Peter Hain welcomed the IMC report as "positive".
"There have been no murders, no recruitments and no bank robberies. Compared to where we were 10 years ago, there has been a sea change," he said.
Mr Hain said there was "enough evidence of progress to make the process of political talks meaningful".
Speaking in the Commons, Prime Minister Tony Blair said: "A fair summary of what the IMC has said is that they draw attention to their belief that there has been a strategic decision by the leadership of the IRA to give up the armed struggle.
"What they have also said, however, is that they are concerned about violence and criminality.
"Let me make it clear once again, all criminal activity has to cease. That is absolutely crucial."
The IMC report comes ahead of talks next week with Northern Ireland's political parties which are designed to try to move the stalled political process forward.
In July 2005, the IRA announced that it had formally ordered the end of its armed campaign.
This statement was further backed up in September when the Independent International Commission on Decommissioning said the organisation had put all of its weapons beyond use.
The Independent Monitoring Commission was set up by the British and Irish governments in January 2004 to monitor the activity of paramilitary organisations.
It also monitors the "normalisation" of security measures in Northern Ireland.
Its four commissioners come from Northern Ireland, the Republic of Ireland, Britain and the US.