OBAMA FOR USA

US President Barack Obama said Sunday that his decision to pour 30,000 more US troops into the war in Afghanistan was the most difficult of his presidency so far.

The newly-crowned Nobel laureate told CBS that the experience of attending ceremonies for fallen soldiers returning home in coffins or visiting scarred veterans of the wars in Iraq and Afghanistan had deeply marked him.

"There is nothing more profound. And it is a solemn obligation on the part of me as commander in chief to get those decisions right," he said.

Just days before he was awarded the Nobel peace prize and after months of deliberations, Obama unveiled his new Afghan strategy in a speech to cadets in the prestigious West Point academy.

"That was actually probably the most emotional speech that I've made, in terms of how I felt about it. Because I was looking out over a group of cadets, some of whom were going to be deployed in Afghanistan. And potentially some might not come back," Obama said.

"There is not a speech that I've made that hit me in the gut as much as that speech."

Asked on CBS "60 Minutes" if the decision to pour more troops into Afghanistan was the toughest yet of his young presidency, he replied: "Absolutely."

But he cautioned against any triumphalist notion of war as he said had occurred during the administration of his predecessor George W. Bush.

"There was a tendency to say, 'We can go in. We can kick some tail. This is some glorious exercise.' When in fact, this is a tough business."

In his first interview since ramping up the war in Afghanistan, Obama also defended himself against criticisms that by setting a July 2011 date for the start of a US withdrawal he was emboldening Al-Qaeda and Taliban militants.

Without a deadline, "the message we are sending to the Afghans is, 'It's business as usual. This is an open-ended commitment,'" Obama said.

By December 2010 it should become clear whether the surge is working, the US president said. "If the approach that's been recommended doesn't work, then yes, we're going to be changing approaches," he added.

Obama acknowledged that his move to send in more troops flew in face of public opposition to war but said he had reach his decision, "because I think it's the right thing to do. And that's my job."

More than 400 foreign troops have died in Afghanistan this year, most of them Americans, making it the deadliest year for US forces in the country since the 2001 US-led invasion, according to the website icasualties.org.

A 1,500-strong Marine contingent is due to arrive in southern Helmand province this week as part of a vanguard of Army and navy engineers set to prepare the logistics for thousands more due in the coming months.

US and NATO commander in Afghanistan, General Stanley McChrystal, told US lawmakers last week he believed the larger US-led force could shift the momentum against the spreading Taliban insurgency.