Nato has agreed to boost troop numbers to cover the Afghan presidential election in August, outgoing alliance chief Jaap de Hoop Scheffer has said.
US President Barack Obama said his alliance partners would deploy about 5,000 troops and trainers "to advance [Washington's] new strategy".
The Nato 60th anniversary summit in Strasbourg picked Danish PM Anders Fogh Rasmussen as new secretary-general.
Anti-Nato protesters fought police and set buildings alight in the city.
They set a hotel and a customs house on fire and three columns of smoke could be seen rising over the Europe Bridge area of the French city, across from the small town of Kehl in Germany, where part of the summit was held.
At least 25 people were arrested, adding to dozens detained in the run-up to the gathering.
Between 10,000 and 30,000 demonstrators were involved in the anti-Nato protests, according to French news agency AFP.
"We will deploy the forces necessary to support the upcoming elections in Afghanistan," Mr de Hoop Scheffer told the news conference after the summit.
It is way too early to judge whether it [the summit] has been successful.
Nato was also providing more trainers and mentors for the Afghan army and police, he said.
"The bottom line is that when it comes to Afghanistan, this summit, and this alliance, have delivered," Mr de Hoop Scheffer added.
Speaking after the secretary-general and before his departure for a summit with EU leaders in Prague, Mr Obama commended fellow Nato members for giving "strong and unanimous" support to his new strategy in Afghanistan.
He said the US was determined to defeat al-Qaeda in Afghanistan and Pakistan.
"All of Nato understands that al-Qaeda is a threat to all of us," he added.
White House spokesman Robert Gibbs said that 900 new troops would come from Britain, 600 from Germany and 600 from Spain. Italy and France were fresh committing forces, too, he added.
Mr Obama has begun the process of tying Nato and Europe firmly into the war in Afghanistan, BBC North America editor Justin Webb reports from Strasbourg.
He has had the opportunity to make the case directly to the European public and privately to European leaders that this war is essential for their safety, our correspondent says.
UK Prime Minister Gordon Brown welcomed promises of extra troops.
OBAMA'S TRANSATLANTIC VISIT
3 April: Obama meets Sarkozy in France and Merkel in Germany
4 April: Leaders walk across the Rhine and hold North Atlantic Council meeting in Strasbourg
"I am pleased to say that a large number of countries have announced that they will provide additional support: Spain, the Netherlands, Portugal, Italy, Greece, Poland, Turkey and Croatia have joined Germany, who have already made similar announcements," he said at the end of the summit.
"That means that burden-sharing over these next few critical months is a reality."
Earlier, German Chancellor Angela Merkel commended Mr Obama's new strategy for Afghanistan, saying: "It fits very well with what we all think."
There are more than 70,000 foreign troops in Afghanistan, mostly under Nato command. Mr Obama is to send 21,000 additional US troops, while considering a further deployment of 10,000.
Mr Rasmussen will take over as Nato chief at the start of August.
NATO: KEY MOMENTS
Founded 1949, largely to block Soviet expansion into Europe
Twenty-six member states who vow to defend each other
Militarily dominated by the US
Acted in non-member state for first time in 1995 - implementing military aspects of Bosnia peace accord
Operated outside Europe for first time in 2003 - in Afghanistan
He was only appointed after a day of sometimes frantic diplomatic exchanges, BBC diplomatic correspondent Jonathan Marcus reports from Strasbourg.
Turkey appeared determined to derail the candidacy of a man backed by all the other Nato allies, seeing Mr Rasmussen as insufficiently sensitive to Muslim concerns after the 2005 Prophet Muhammad cartoon row.
The Turkish government was also angered by the operation of a television station on Danish soil that it accused of being a mouthpiece for Kurdish guerrillas - but the pressure on Turkey was enormous, our correspondent says.
His election was confirmed by Mr de Hoop Scheffer who said:
"You know that there has been discussion over the past 36 hours but the fact that we are standing here next to each other means a solution has been found also for the concerns expressed by Turkey, and we all very much agree and are unanimous."
Mr Rasmussen said he planned to step down as prime minister within days and wanted his Finance Minister, Lars Lokke Rasmussen, to take over from him.
Turkish PM Recep Tayyip Erdogan said his country had agreed to drop its opposition to Mr Rasmussen's candidacy after receiving unspecified "guarantees" from President Obama.
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