London, Jan 22 (Agencies): Former Prime Minister Tony Blair told Britain's Iraq war inquiry that the world had to use force if needed to curb Iran's nuclear drive and expressed regret at the death toll from the 2003 conflict.

Blair also said US President Barack Obama's approach to Tehran was failing during his second appearance before the inquiry.

The former premier, now Middle East peace envoy, was at his most animated when talking on Friday about Iran's influence in the region, which he condemned as negative and destabilising.

"Iraq is one part of a far bigger picture and right across that region, people are facing that struggle," he said.

"This is a looming and coming challenge," he said. "At some point, we've got to get our head out of the sand.

"The West has got to get out of this wretched posture of apology for believing we are causing what these Iranians are doing, or what these extremists are doing. We are not."

He said Obama's appeal to Iran in his 2009 Cairo speech had got nowhere.

"They carry on with the terrorism, they carry on with the destabilisation, they carry on with the nuclear weapons," he said.

"They'll carry on doing it unless they are met by the requisite determination and if necessary, force."

An emotional Blair addressed the condemnation he faced following his first hearing last January when he said he had "no regret" about removing Iraqi dictator Saddam Hussein.

"That was taken as my meaning that I had no regrets about the loss of life and that was never my meaning or my intention," he said.

"I wanted to make that clear that of course I regret deeply and profoundly the loss of life, whether from our own armed forces, those of other nations, the civilians who helped people in Iraq or the Iraqis themselves."

His words sparked an angry response from the packed public gallery, where relatives of some of the 179 British soldiers killed in Iraq were sitting.

"Your lies killed my son, I hope you can live with yourself," shouted Rose Gentle, whose 19-year-old son Gordon was killed in 2006 while serving in Basra, as Blair left the hearing.

Outside the central London venue, dozens of anti-war demonstrators protested.

The inquiry, aimed at learning lessons from the Iraq war, was launched after the withdrawal of British troops from the country in July 2009. Blair, who was prime minister from 1997 to 2007, has been its star witness.