The US military also says it has about 17,000 US troops under sole US command charged with fighting Taleban and al-Qaeda insurgents.
The Kyrgyz parliament voted in favour of closing the Manas air base by 78 votes to one.
Manas is currently the sole US air base in Central Asia
If President Kurmanbek Bakiyev signs the bill, the US will have 180 days to leave the base - its only one in Central Asia.
Critics say Kyrgyzstan is closing the US base in return for financial aid offered by Moscow but Kyrgyz officials say the two events are unrelated.
While Russia is allowing the transit of Afghan-bound cargo through its territory, the closure of the only US military base in Central Asia indicates that the Kremlin still has the upper hand in the politics of some of its former republics, the BBC's Rayhan Demytrie reports from the Kyrgyz capital, Bishkek.
Pentagon spokesman Bryan Whitman said the US was still looking at what it could offer Kyrgyzstan to keep the air base open.
But he added: "We're not prepared to stay at any price and we continue to look at other options."
Meanwhile, a delegation of US military transportation officials has arrived in Dushanbe, capital of the central Asian republic of Tajikistan, to evaluate that country's potential as a transit corridor to Afghanistan.
America recently invested millions of dollars in a bridge connecting the two countries and may be looking at using it to transport its own supplies.
'Tough' year ahead
America's top commander in Afghanistan, Gen David McKiernan, has predicted that the coming year will be "tough".
FROM THE TODAY PROGRAMME
Some countries have indicated that they may be able to offer more help over the spring and summer to improve security ahead of the poll.
UK Defence Secretary John Hutton told the BBC that Nato's European allies needed to do more to ensure a fairer burden-sharing of responsibilities in Afghanistan.
Britain is the second biggest contributor to the Nato-led mission, with more than 8,000 troops deployed in Afghanistan.
However, there is a growing realisation in the US and UK that allies such as Germany, France and Italy are unlikely to offer significant numbers of extra combat forces, or change the nature of their missions, says the BBC's Caroline Wyatt in Krakow.
But those countries unwilling or unable to send more combat troops will also be pushed for extra help and funding on the civil side, focussing on governance, police training and the fight against drugs, our correspondent says.
Speaking on board a US military plane en route to the two-day Nato meeting, Mr Gates said the new US administration was "prepared... to make additional commitments to Afghanistan, but there clearly will be expectations that the allies must do more as well".
He said the response so far to requests for allies to supply extra troops ahead of elections had been "disappointing".
Mr Hutton has rejected claims that some US military commanders are unhappy with the performance of the British troops in Afghanistan.
In an interview with the Financial Times newspaper, Mr Hutton said: "I do not think that is fair, nor do I think that reflects the real view in the Pentagon and elsewhere.
"There is a very high level of regard for the contribution that UK forces have made in Iraq and Afghanistan.
"We will not change our tactics in Afghanistan on the basis of uncorroborated and unsourced gossip from people who don't have the courage to put their names to their remarks," Mr Hutton said.
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