Prime Minister Tony Blair has rejected demands for an independent inquiry into leaks of police anti-terrorism intelligence to the media.
The Conservatives and Liberal Democrats have both asked the government for a formal investigation.
The UK's counter-terrorism chief has said leaks could "put lives at risk".
But Mr Blair said "as far as he was aware" ministers and civil servants had not been responsible for any, and he completely condemned all leaks.
On Tuesday Deputy Assistant Commissioner Peter Clarke of the Metropolitan Police said people who divulged sensitive information to the media were "beneath contempt".
But he did not specify where the leaks had come from.
Instead he used a recent anti-terror investigation in Birmingham as an example of when information had been leaked to the media.
Shadow home secretary David Davis has asked Cabinet Secretary Sir Gus O'Donnell to launch a formal inquiry into this operation.
The Lib Dems have written to West Midlands Chief Constable Paul Scott-Lee, asking his force to begin an investigation.
During prime minister's questions in the Commons, Tory leader David Cameron called on Mr Blair to appoint an independent person to investigate leaks.
He asked for assurances that no minister, civil servant or special adviser had divulged information.
Mr Blair said: "The only guarantee that I can give is that, as far as I'm aware, they did not.
"But let me make it absolutely clear that I completely condemn any leaks of sensitive information from whatever quarter."
He criticised Mr Cameron for his suggestion that members of the government were responsible.
"I don't think it's right to leave an allegation suggesting that may be a minister who has done this, unless he's got actual evidence that that is so.
"But I would have thought that everyone would understand that when the police, particularly when they are conducting very sensitive operations - and where there's the potential for the significant loss of life - then it's incredibly important that that information is kept confidential and tight.
"As far as I'm concerned, that is the case."
A spokesman for the Conservative Party later told the BBC they had "no evidence" any minister or civil servant was involved in leaking details of the Birmingham investigation.
He said Mr Cameron had not made any accusation, but wanted an inquiry to clear the issue.
In the Commons Mr Blair agreed with DAC Clarke's stance that there was no justification for ever leaking such information.
DAC Clarke had said there were a "small number of misguided individuals who betray confidences".
By doing so, they had compromised investigations, revealed sources of life-saving intelligence and "put lives at risk" during major investigations.
Dame Pauline Neville-Jones, the former head of the Joint Intelligence Commitee, told Channel 4 News it was a "very serious" matter and she thought the government should investigate.
Lib Dem leader Sir Menzies Campbell told the BBC: "It may be for all we know that there have been some breaches of the criminal law.
"There may even have been breaches of the Official Secrets Act. If that is so, then the proper investigating authority in the first instance would be the police themselves."