The Kyrgyz government sent parliament a decree on closing the Manas base on Wednesday.
Adakhan Madumarov, secretary of the Kyrgyz Security Council, said in Moscow that the U.S. military would be given 180 days to close its operations and leave once the two sides had exchanged formal diplomatic notes outlining the intention.
"The government has made its decision," he told reporters without saying when the exchange was likely to happen.
Parliament sources said it could start debating the decree as soon as Thursday. Parliamentary approval is seen as a formality since the chamber is dominated by the pro-presidential Ak Zhol party.
U.S. military personnel will be given 180 days to close operations and leave once the final decision is made.
Kyrgyz President Kurmanbek Bakiyev announced that the base would be shut after securing Russian financial aid at talks on Tuesday in Moscow, which wants to reduce U.S. influence in regions it considers part of its traditional sphere of interest.
The decision sends a tough signal and challenge to new U.S. President Barack Obama as he plans to send additional troops to Afghanistan. The base is an important staging post for the U.S.-led military campaign against the Taliban, and its role has been heightened as Washington seeks to reinforce supply routes that bypass Pakistan, where militants severed the main route into Afghanistan by blowing up a bridge in Pakistan's Khyber Pass this week.
U.S. officials said talks on the base were still under way.
"We have been discussing the base with Kyrgyz authorities for some time now. We hope those discussions will continue to the point where we reach some mutually beneficial outcome," said Pentagon spokesman Geoff Morrell.
Moscow, which operates its own air base in Kyrgyzstan a few dozen kilometers away from Manas, has long been irritated by the presence of U.S. troops and has put pressure on Kyrgyzstan to close Manas.
During his visit to Moscow, Bakiyev received a promise of more than $2 billion in credit and aid from Russia to combat an economic crisis -- the equivalent of about half of impoverished Kyrgyzstan's gross domestic product.
Outside Bishkek, business appeared as usual at the air base, with no unexpected activity seen from behind barbed wire encircling the facility, home to more than 1,000 U.S. military personnel.
At its main gate, three servicemen refused to talk to reporters.
Outside Manas, surrounded by swathes of empty land, a Kyrgyz sheepherder said he supported closing the base -- partly because he wanted more grazing land.
"I support this move. We think this air base only harms our nature," said Ulan, a bearded man of about 50.
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