Mrs Clinton said there had been a "positive" response from allies
US Secretary of State Hillary Clinton says she is confident Nato countries will pledge extra troops to help efforts in Afghanistan.
"The response has been positive," Mrs Clinton said as she headed to Brussels, where she is joining Nato talks.
Nato officials said on Thursday that more than 20 countries plan to send more troops following a US decision to deploy an extra 30,000 in Afghanistan.
But several European nations have been reluctant to commit more forces.
The BBC's Nick Childs, in Brussels, says a number of nations - including Italy, Poland, Georgia and Britain - have gone public with their intention to send more forces.
US calling for about 10,000 extra foreign troops
Nato expects 5,000 troops from 20 of 43 nations in Afghanistan
Not all have gone public with their intentions
Britain has pledged extra 500; Italy "about 1,000"; Poland 600; Portugal 150; Spain 200; Solvakia 250; Macedonia 80
Non-Nato member Georgia sending 900, South Korea 500
France still considering response; Germany may delay decision until January 2010
But US officials would clearly like a few more to do so by the end of these two-day talks, our correspondent says.
Many Nato governments face publics even more sceptical about the mission than those of the US and Britain, and some major allies, like France and Germany, are holding off.
But even if more public announcements are forthcoming, turning these into firm pledges of the right troops at the right time and for the right missions, may take longer, our correspondent adds.
Mrs Clinton said she had engaged in "intensive outreach" with fellow foreign ministers in the wake of a request by US President Barack Obama for Nato allies to send some 10,000 more troops.
"There's an understanding about the importance of the mission that the president has described, there is a desire to be able to explain it to the publics of various countries," Mrs Clinton said.
She acknowledged that in some cases the "political stars" may not yet be aligned to allow for public statements of additional support, but she said US officials felt "good" about bringing other nations on board.
Speaking on Thursday, Nato spokesman James Appathurai said: "There are well over 20 countries that are indicating or have already indicated that they intend to increase their troops numbers in Afghanistan.
The US wants Nato allies to increase their troop numbers
"Based on what we have heard in the last 24 hours... we are beyond the 5,000 figure."
However, he said there were still "significant shortfalls" of army and police trainers.
The full extent of additional resources coming from Nato allies remains unclear.
Italian Defence Minister Ignazio La Russa told the Corriere della Sera newspaper on Thursday that Rome would send about 1,000 extra troops to Afghanistan. It currently has 3,200 soldiers there.
Russian President Dmitry Medvedev, speaking after a meeting with Italy's Prime Minister Silvio Berlusconi, indicated that Russia would also do its part in Afghanistan.
"We are ready to support these efforts, guarantee the transit [of troops], take part in economic projects and train police and the military," he said.
But while the German parliament voted to extend by a year the mandate allowing the government to send troops to Afghanistan, it did not lift the upper limit of soldiers, currently set at 4,500.