BARACK Obama pledged "humility and restraint" in US foreign policy as he assumed the presidency today.

In a speech that included several digs at the military unilateralism of George Bush's leadership, Mr Obama said the US could not do "as it pleased" and reached out to "former foes" and the Muslim world.

But he also delivered a stark warning to terrorists that he would not "waver" in defending the American way of life: "You cannot outlast us, and we will defeat you."

Mr Obama said earlier generations had faced down communism and fascism "not just with missiles and tanks, but with sturdy alliances and enduring convictions".

"They understood that our power alone cannot protect us, nor does it entitle us to do as we please," he insisted.

"Instead, they knew that our power grows through its prudent use; our security emanates from the justness of our cause, the force of our example, the tempering qualities of humility and restraint."

US troops will be "responsibly" withdrawn from Iraq, and a "hard-earned peace" would be forged in Afghanistan, according to Mr Obama.

"With old friends and former foes, we will work tirelessly to lessen the nuclear threat, and roll back the spectre of a warming planet," he added.

The US was "ready to lead once more", and be the friend of everyone who sought "peace and dignity".

Mr Obama made a point of addressing the Muslim world, calling for a "new way forward, based on mutual interest and mutual respect".

In a hint at his future approach towards states like Iran and Zimbabwe, he insisted leaders who clung on to power through "corruption and deceit and the silencing of dissent" were on the "wrong side of history".

But he signalled he was still willing to talk to them: "We will extend a hand if you are willing to unclench your fist."

The new President insisted America would not "apologise" for its way of life, or "waver in its defence".

He went on: "For those who seek to advance their aims by inducing terror and slaughtering innocents, we say to you now that our spirit is stronger and cannot be broken; you cannot outlast us, and we will defeat you."

Mr Obama also indicated that he would be focusing on the developing world and tackling poverty.

America would help people in poor nations to "make your farms flourish and let clean waters flow", he said.