The US is investigating Iraq National Congress chief Ahmad Chalabi's role in revealing to Iran sensitive information about the intelligence inputs obtained by Americans in Iraq, a media report said on Monday.

"The FBI has begun reviewing logs and data that might turn up clues as to when sensitive information was divulged. The officials are also interviewing and giving lie-detector tests to US officials in Iraq who may have had access to the information," US officials told Time magazine.

The report said that the White House has been steadily losing patience with its former client. The beginning of the end came in February when Chalabi was quoted in a London daily as saying that even if the intelligence about Saddam Hussein's weapons programme that he passed to the US before the war was faulty, it was "not important" compared to the end result of toppling the Iraqi dictator.

"We were heroes in error," he was quoted as saying.

According to Time, though Chalabi insisted that he was misquoted, the damage was done. "That set the president off," a senior administration official told Time. The general feeling among top officials was that "we gotta do something about this guy".

Iraq expert Robert Blackwill was commissioned to draft a plan to cut ties with Chalabi, the report said.

State department and CIA officials, who have long criticised the intelligence inputs provided by Chalabi, endorsed Blackwill's recommendations.

Chalabi had also fallen out with Ambassador Paul Bremer, a US official in Iraq said. An Iraqi judge issued a search warrant into alleged theft of property and government vehicles by INC members, Time reported.

However, the search was stymied, as police couldn't get into INC offices the first time they went.

Defence Intelligence Agency officials working in a Pentagon-funded intelligence programme attached to Chalabi's group stopped the officers at the door, arguing that the sensitive intelligence information needed to be protected.

On May 13, after the administration decided to cut off the $335,000 monthly subsidy to the INC, the DIA agents vacated the INC office.

Bremer sent the police back a week later, backed by US soldiers.

However, Bremer denied having prior knowledge of the raid, but Time quoted sources as saying he authorised it. Bremer didn't inform the White House or the Pentagon of the timing of the move, an official said, but Chalabi has few allies left in Washington willing to defend him.

"Nobody can protect anyone anymore," a Pentagon official said.