Nato has agreed to boost troop numbers to cover the Afghan presidential election in August.
United States President Barack Obama, speaking at Nato's summit in Strasbourg, France, said his alliance partners will deploy about 5,000 extra troops and trainers.
White House spokesperson 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.
There are more than 70,000 foreign troops in Afghanistan, mostly under Nato command.
New man at the top
At the meeting, NATO leaders chose the Danish prime minister, Anders Fogh Rasmussen, as their next Secretary-General despite some opposition to his appointment.
His candidacy was opposed by Turkey, which was unhappy with the way he handled the row over Danish cartoons of the Prophet Mohammed.
The largely Muslim country had threatened to veto his appointment but eventually bowed to pressure from the United States, France and Germany.
Protesters fight police
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.
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.