US Vice-President Dick Cheney has held talks with Afghan President Hamid Karzai on a visit to Kabul.
Mr Cheney (L) urged Nato allies to increase troop numbers
Mr Cheney called on other Nato countries to increase their commitment to Afghanistan's security in the face of a growing threat from the Taleban.
It is Mr Cheney's fourth trip to the country as vice-president.
He arrived there from Iraq, where his visit coincided with the fifth anniversary of the US-led invasion of the country.
"America will ask our Nato allies for an even stronger commitment for the future," said Mr Cheney.
"The United States and the other members of the coalition need to have a sufficient force here... to deal with the threat [from] the Taliban and al-Qaeda," he added.
US troops make up a third of the Nato-led International Security Assistance Force (Isaf).
A further 7,000 troops are part of a US-led coalition there, and some 3,200 Marines scheduled for a seven-month deployment in the south have begun arriving in Kandahar.
Afghanistan will be a key topic at a Nato summit early next month in Romania, as Nato force commanders have asked for more troops to send to the south, where the insurgency is the most active.
The US has been putting pressure on Nato allies Germany and France to allow their troops to move away from the relatively safe northern Afghan provinces and assist troops from the US, UK, Canada and the Netherlands fighting in the south.
Canada, which has more than 2,000 troops in the south, has threatened to pull out unless Nato provides another 1,000 soldiers to reinforce its combat forces.
During the visit, Mr Cheney also spoke about the results of neighbouring Pakistan's recent election.
He told reporters that he expected the new government in Pakistan to be "good and effective friends and allies of the United States".
Pakistan is set to have a new coalition government comprising opponents of President Pervez Musharraf, a staunch US ally in the "war on terror" who has become increasingly unpopular domestically.
"I have no reason to doubt their commitment to dealing with the problems that emerge," Mr Cheney said.
The US and Afghanistan have repeatedly asked Pakistan to take action against pro-Taleban militants based along the country's rugged border with Afghanistan.