Nato chiefs have agreed to meet again during the coming days to decide who is to supply extra soldiers and equipment needed for operations in Afghanistan.
Nato wants bigger contributions to the Afghan campaign
Talks in the Polish capital, Warsaw, resulted in agreement that more troops were needed for the Afghan campaign.
Military Committee Chairman Gen Ray Henault told defence chiefs in Warsaw that while Nato had 85% of its required force, casualties were mounting.
Currently 18,500 Nato troops are stationed in Afghanistan.
Nato military commanders say they need another 2,500 troops to carry out their mission, amid intense clashes with Taleban rebels in the south.
BBC defence correspondent Paul Wood says this is far more than Nato officials were suggesting only a few days ago - and an indication of how much tougher the fight with the Taleban has become.
On Saturday Nato-led forces in Afghanistan said they had killed more than 40 Taleban militants in a continuing offensive in the southern province of Kandahar.
The latest clashes bring to about 300 the number of insurgents killed since the operation began a week ago, Nato says.
Reporters have been unable to visit the scene to verify casualty figures.
A number of Nato soldiers, most of them British or Canadian, have been killed in recent weeks.
Gen Henault urged member states to send "all the people and the capability" that had been signed up to.
"We are currently at about 85% of the requirements and want the remainder," he was quoted as saying by AFP news agency.
No further pledges of troops have so far been made.
Officials from Turkey, Germany and Italy have expressed reluctance to move their troops from reconstruction work in safer parts of Afghanistan to the troubled south, our correspondent adds.
There are more than 20,000 American troops in Afghanistan at the moment, but only around 2,000 of them currently under Nato command.
When Nato's International Security Assistance Force takes control of the east as well, in the next few weeks, a major chunk of the US forces will transfer to the command of Nato.