US President Barack Obama has warned that al-Qaeda was a greater threat to Europe than the US.
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Speaking before a NATO summit in Strasbourg, Mr Obama urged better use of NATO resources in Afghanistan, and called on the developed world to take the lead in tackling climate change.
He also warned of the dangers associated with the spread of nuclear weapons.
The summit is jointly hosted by the French city of Strasbourg and its German counterparts, Baden-Baden and Kehl, on the other side of the Rhine River.
Mr Obama helped broker a deal at a G20 summit in London yesterday to tackle the global financial crisis and will be hoping for a similarly broad accord at the two-day NATO summit on how to turn the tide against the worsening Afghan crisis.
The US leader unveiled a new Afghan strategy last week that aims to get a grip on rising violence by Taliban militants driven from power in 2001 but never completely defeated.
It broadens the focus to include Pakistan and puts the highest priority on the defeat of al-Qaeda militants who Mr Obama says are plotting new attacks on the US.
Having already announced plans to add 17,000 US combat troops to the 38,000 already there, Mr Obama said he would send 4,000 more to help train Afghan officials to combat problems such as the booming narcotics trade and government corruption.
British Prime Minister Gordon Brown has also offered to send additional British troops to Afghanistan to provide security during the forthcoming presidential election.
The NATO mission has been criticised for disorganisation but European leaders have been reluctant to commit more forces to a war that is increasingly unpopular with voters.
The NATO summit, co-hosted by Germany and France, starts with a dinner in the evening across the border in Baden-Baden.
Mr Obama has said countries that felt unable to commit more military forces to Afghanistan should at least boost help for the civilian effort.
NATO Secretary-General Jaap de Hoop Scheffer has called on other allies to send up to 4,000 more troops to safeguard August elections. He also wants them to make up a shortfall in training teams for the Afghan army and police force.
Demonstrators clash with police
Anti-NATO demonstrators have vowed to disrupt the summit and riot police clashed with hundreds of protestors yesterday in Strasbourg, repeatedly firing tear gas and rubber bullets and arresting around 300 youths.
This morning 300 demonstrators were arrested.
German and French authorities expect some 40,000 peace activists to stage protests at the summit and authorities expect up to 20,000 demonstrators at the main anti-NATO rally in Strasbourg on 4 April.
Up to 15,000 police and troops in each city will be deployed to protect the NATO leaders, who include US President Barack Obama.
