WASHINGTON - THE chairman of a House intelligence oversight committee plans to ask for a US government investigation into whether the National Security Agency (NSA) illegally withheld evidence from lawyers who unsuccessfully defended an American Muslim scholar from terrorism charges, according to the lawmaker's spokesman.

Representative Rush Holt, chairman of the House Appropriations Select Intelligence Oversight Panel, is expected this week to ask the National Security Agency inspector general to investigate whether the NSA failed to hand over wiretapping records requested by Ali Al-Timimi's defence lawyers, who believed him to be under surveillance by the so-called warrantless wiretapping programme.

Al-Timimi was subsequently convicted and is now serving a life sentence on terrorism related charges.

Al-Timimi was convicted in 2005 of encouraging followers in the days after the Sept 11 attacks to join the Taleban and fight US troops.

President George W. Bush has acknowledged that within days of the Sept 11 attacks he authorised the National Security Agency to conduct warrantless intercepts of conversations between people in the United States and others abroad who had suspected ties to Al-Qaeda or its affiliates.

This was done without the knowledge or approval of the Foreign Surveillance Intelligence Court, created by Congress 30 years ago to oversee just such government activity.

Al-Timimi's lawyer, Jonathan Turley, has been seeking wiretap recordings he believes were made of his client by the government between Sept 11, 2001, and Feb 1, 2003.

The government has claimed it has no relevant wiretap recordings during that time period and says it has turned over everything relevant.

Mr Turley, who has a security clearance and has been given access to details of the NSA's wiretapping programme, says that is untrue.

In a Dec 4 letter, Mr Turley says earlier this year he was allowed to see previously undisclosed evidence that showed some of the NSA intercepts he had specifically requested for the 2005 trial existed but had not been handed over.

The Justice Department lawyers prosecuting the case did not have the security clearances to know about the intercepts.

'There is compelling evidence to suggest that individuals in this administration knowingly withheld evidence in this case and knowingly allowed an uncleared prosecutor to make false representations in court,' Mr Turley wrote.

The newswires obtained Mr Turley's letter to House Intelligence Committee Chairman Sylvestre Reyes, a Democrat, on Monday. -- AP