LONDON — Ex-secretary of state Colin Powell called on the CIA and Pentagon to explain how he was given unreliable information which proved key to the US case for invading Iraq, the Guardian reported Wednesday.

Powell's landmark speech to the United Nations on February 5, 2003, cited intelligence about Iraq leader Saddam Hussein's bioweapons programme gained from a defector, codenamed Curveball.

But he has now admitted that he lied to topple the dictator, in an interview with the Guardian.

"It has been known for several years that the source called Curveball was totally unreliable," Powell told the British newspaper.

"The question should be put to the CIA and the DIA (Defense Intelligence Agency) as to why this wasn't known before the false information was put into the (report) sent to Congress, the president's state of the union address and my 5 February presentation to the UN."

The defector, real name Rafid Ahmed Alwan al-Janabi, told the Guardian that he lied to the BND, Germany's secret service, by claiming in 2000 that Iraq had mobile bioweapons trucks and had built clandestine factories.

During Powell's speech, Janabi was described as "an Iraqi chemical engineer" who "supervised one of these facilities."

"He actually was present during biological agent production runs and was also at the site when an accident occurred in 1998," Powell told the UN.

Janabi was exposed as an unreliable source when the BND visited Bassil Latif, his former boss at the Military Industries Commission in Iraq, who said there were no trucks or factories.

However, the BND continued to cooperate with the trained chemical engineer, and the false statements were eventually passed on to senior US policymakers by the intelligence services.

The resulting conflict claimed more than 100,000 civilian lives and ruined the political standing of the then US president George W. Bush and his defence secretary Donald Rumsfeld.

Hans-Christian Stroebele, a Green deputy in Germany's federal parliament, told the Guardian Janabi had arguably broken the German law which forbids warmongering.