http://news.bbc.co.uk/2/hi/americas/7966982.stmUS President Barack Obama has confirmed a fundamental rethink of US strategy in Afghanistan and Pakistan to combat an "increasingly perilous" situation.
He said growing radical forces in the area posed the greatest threat to the American people and the world.
He said an extra 4,000 US personnel would train and bolster the Afghan army and police, and he would also provide support for civilian development.
Both Pakistan and Afghanistan said they welcomed the new strategy.
Pakistani Prime Minister Asif Ali Zardari said it would strengthen democracy in his country, while the Afghan government said Mr Obama had recognised that the al-Qaeda threat came mainly from Pakistan, and that it was a regional problem.
See map of troop deployments in Afghanistan
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Bleak picture
President Obama said his "comprehensive new strategy" was an outcome of a "careful policy review" in which military commanders and diplomats, regional governments, partners, Nato allies, NGOs and aid organisations were consulted.
He painted a bleak picture of the situation, with insurgents increasing their control of territory in the region around the Afghan-Pakistan border - which he termed "the most dangerous place in the world" for the American people - and attacks rising.
He said American strategy must relate directly to the threat posed to the Americans by al-Qaeda and its allies - who, he reminded his listeners, were behind the 9/11 attacks on American soil eight years ago.
And he said multiple intelligence estimates suggested fresh attacks on the US were being planned.
But he said targeting al-Qaeda was not only in the interests of American people, but populations around the world and Afghans themselves.
"This is not simply an American problem. Far from it," Mr Obama said.
"It is instead an international security challenge of the highest order."
He said US forces should not be in Afghanistan to "control that country or dictate its future", but to "confront our common enemy".
In an interview before Mr Obama's speech, with the BBC's Andrew Marr, the Russian President Dmitry Medvedev said Moscow was "ready to participate in the efforts directed at putting things in order" in Afghanistan.
But he said a key target must be to achieve a "normal political system in place in Afghanistan".
"It is impossible to rule Afghanistan with the aid of the alliance; it is impossible to rule Afghanistan from abroad. Afghanistan should find its own path to democracy," Mr Medvedev said.
Civilian infrastructure
To achieve its goals, Mr Obama said, the US needed:
A "stronger, smarter and more comprehensive strategy"
Not to deny resources to Afghanistan because of existing commitments to Iraq - and here international help was needed
To recognise the connection between the future prospects of Afghanistan and Pakistan
He said that Richard Holbrooke had already been appointed as the US envoy to both Afghanistan and Pakistan in order to facilitate this new shared perspective on both countries.
In Afghanistan, Mr Obama said a further 4,000 US troops would help train up the Afghan army and police - in addition to the 17,000 troops whose redeployment to Afghanistan has already been announced.
They will join some 38,000 US forces already on the ground.
Mr Obama said more help for training would also be sought from Nato allies, in order to build an Afghan army of 134,000 and a police force of 82,000.
And to help reinforce Afghanistan's crumbling civilian infrastructure, he said, hundreds of US advisers including agricultural specialists, engineers and lawyers would be sent to the country.
He said this would help address the Afghan's government problems with corruption and the delivery of basic services.
Speaking after the president's announcement, Ambassador Holbrooke said some US allies had already privately promised extra troops for the region.
'Not just bombs'
In Pakistan, Mr Obama said American help would be needed to go after al-Qaeda, which Mr Obama admitted was "no simple task".
But he said this would not amount solely to "bombs and bullets", adding that the success of this plan depended on the strength of the embattled Pakistani government.
So, he said, he was calling upon Congress to pass a bill authorising a tripling of US spending in Pakistan to $1.5bn (£1.05bn) each year over the next five years, to help rebuild "schools, roads and hospitals".
But he said this was "no blank cheque" - and Pakistan would have to demonstrate its own commitment to rooting out the "cancer" of al-Qaeda and its allies.
The instability there was underlined on Friday, when a bomb attack on a mosque in north-west Pakistan killed dozens of people.