'Fighting al Qaeda is more important than the war in Iraq,' says Obama as he pledges troop pull-out by 2010

The White House nominee used a major policy speech to say he would deploy at least two combat brigades to Afghanistan and withdraw all US troops from Iraq within 16 months of reaching the White House - denying accusations that he was wavering on his plan to bring U.S. troops home within 16 months if he is elected president.

The Illinois senator also promised to put pressure on Pakistan to do more to fight al Qaeda and the Taliban.

Foreign policy: A volunteer holds U.S flags and a poster supporting Barack Obama in Newport Beach, California

'This war diminishes our security, our standing in the world, our military, our economy, and the resources we need to confront the challenges of the 21st century,' he said.

'By any measure, our single-minded and open-ended focus on Iraq is not a sound strategy for keeping America safe.'

Despite the recent focus on domestic issues with the slumping U.S. economy, the future of Iraq promises to be a central issue in the election battle.

Mr Obama blasted John McCain, his Republican rival in November's White House election, and President Bush for losing goodwill around the world with their dogged determination to fight on in Iraq.

'I am running for president of the United States to lead this country in a new direction -- to seize this moment's promise,' he said. 'As president, I will make the fight against al Qaeda and the Taliban thetop priority that it should be. This is a war that we have to win.'

Drawdown: Mr Obama wants to withdraw U.S. forces from Iraq by 2009

Obama also promised a renewed effort to seize nuclear materials from terrorists and "rogue" nations, and said he would be willing to use 'all elements' of U.S. power to pressure Iran on its nuclear programme.

Obama asked members of his audience to imagine what might have been done after the Sept. 11 attacks, when much of the world was united in support of the U.S.

"Instead, we've lost thousands of lives, spent nearly a trillion dollars, alienated allies, neglected emerging threats -- all in the cause of fighting a war for well over five years in a country that had absolutely nothing to do with the 9/11 attacks,'' he said. "This war diminishes our security.''

Obama, 46, also pledged to widen the focus of U.S. foreign policy to other regions.

"I want to use all elements of American power to keep us safe and prosperous and free,'' he said. "I intend to pursue a tough, smart and principled national security strategy, one that recognises that we have interests beyond Baghdad, in Kandahar and Karachi, in Tokyo and London, in Beijing and Berlin.''

In his speech, Obama said U.S. troops have "performed brilliantly in lowering the level of violence'' in Iraq. Still, he said, that doesn't weaken his argument that the U.S. should begin reducing its role and turning over more responsibility to the Iraqis.

The strain on the military has increased because of the surge, he said, and that has left the U.S. unable to put more resources into Afghanistan, where attacks by extremists and militants made June the deadliest month for the U.S. and its allies since the conflict began in 2001. 

No turning back: Republican presidential candidate Senator John McCain

The recent upsurge of violence in Iraq  continued yesterday when 30 people died in two suicide bombings in Baghdad and another 12 were killed in the northern Iraqi city of Mosul.

A Washington Post/ABC News poll showed voters were evenly split over which candidate they trust to handle the war as an effective commander-in-chief.

Mr Obama has highlighted the resurgence of the Taliban in Afghanistan as a threat that has been harder for the United States to tackle because of the distraction of the Iraq war.

He has proposed adding two U.S. combat brigades, about 9,000 troops, to the 36,000 troops already in Afghanistan and said this would be made possible by a drawdown of troops from Iraq.

'I have argued for years that we lack the resources to finish the job because of our commitment to Iraq,' Obama said in the speech.

Mr McCain, 71, said his rival should consult with military chiefs in the region before speaking out.

Mr Obama claims he has opposed the Iraq war from the start. Unlike Mr McCain and his former Democrat primaries opponent Hillary Clinton, the Illinois senator voted against the 2003 invasion.

Mr McCain criticized Obama for giving a speech on Iraq before travelling there.

Mr Obama's visit to Iraq, where he has only been once, in 2006, and Afghanistan follows repeated criticism from Mr McCain that he should visit the area and talk to commanders. 'Senator Obama is departing soon on a trip abroad that will include a fact-finding mission to Iraq and Afghanistan,' said the Arizona senator.

'And I note that he is speaking today about his plans for Iraq an Afghanistan before he has even left.  In my experience, fact-finding missions usually work best the other way around: first you assess the facts on the ground, then you present a new strategy.'