LONDON — Former prime minister Tony Blair knew that invading Iraq in 2003 could increase the threat from Islamic extremism but pressed ahead nonetheless, a former top civil servant said Wednesday.

Speaking at a public inquiry into Britain's role in the controversial war, David Omand added that a claim Saddam Hussein could launch weapons of mass destruction (WMDs) in 45 minutes aimed to add "local colour" to a 2002 dossier.

Omand, who was the government's security and intelligence coordinator, spoke days before Blair himself makes a hotly anticipated appearance at the probe on January 29.

A key intelligence committee warned in reports in 2002 and 2003 that taking military action in Iraq would increase the risk of Al-Qaeda attacks on Western targets and fuel radicalisation, Omand said.

Blair, though, was still keen to press ahead with the invasion which saw Britain standing shoulder-to-shoulder with the US, he added.

"We knew it was going to be an additional risk but that didn't outweigh the policy objective in his mind," he said.

"I know exactly what he would say which was: 'Yes, that was a risk which we have to take on the chin'".

In the worst attack by Islamist militants in Britain since the Iraq war, 52 innocent civilians died in London in July 2005 when four men carried out suicide bombings on the city's public transport system.

On the 45 minute claim in an official dossier in September 2002 which was widely reported by media at the time although WMDs were not found in Iraq, Omand said he had failed to spot the problems it would cause.

"With hindsight, one can see that adding a bit of local colour like that was asking for trouble but we didn't really spot that at the time," he said.

Omand's evidence at the public inquiry in London came amid appearances by a string of current and former cabinet ministers in the coming days.

Jack Straw, who was foreign secretary at the time of the invasion and is still in government as justice secretary, takes the stand Thursday.