By Paul Reynolds
World affairs correspondent, BBC News website
Inside the US base in Kyrgyzstan
The closure of the Manas US airbase in Kyrgyzstan would be a severe blow to the conduct of the war in Afghanistan.
It is the only US base in Central Asia, and not only is it used for combat sorties - it is a key link in the supply chain which is expected to be used increasingly heavily as a build-up of US reinforcements into Afghanistan develops.
The threat to its future came in a statement from Kyrgyzstan's President Bakiyev, who said in Moscow that his government had decided to close the base. This has been followed by a vote in the Kyrgyzstan parliament to shut down Manas within 180 days of the US being given formal notification to quit.
The US says it has not been given any notification and of course, there is a get out clause there, as the Kyrgyz government might simply delay such an action indefinitely. It nearly asked the Americans to leave in 2005. However this time it appears to be more serious.
The base, attached to Bishkek's airport, was set up in 2001 for the war against the Taleban in Afghanistan.
President Bakiyev was speaking after agreeing an aid package with Russia that would provide more than $2bn of help to his impoverished country. Much of it in would be in the form of an investment in a dam needed for electricity supply but there is also about $450m in grants and soft loans desperately needed to support the country's economy.
Given that its annual budget is just over $1bn, money in this case is obviously vital. And money might have talked as well.
Some observers believe that President Bakiyev has either agreed to Russian demands to link its aid to the closure of the US base or is playing one side off against another.
The future of the Manas base is a test of will for the United States
Under Vladimir Putin, Russia has been trying to reclaim the influence it once had in the former Central Asian Soviet republics, so Russian pressure on Kyrgyzstan is not unexpected.
The US already pays an annual rent of $60m for Manas and other payments bring US aid up to over $150m. It has been in discussions with the Bishkek government about future arrangements.
Matter of money?
"The threat to close Mamas is credible but it is not a guarantee," said Paul Quinn-Judge of the analytical organisation the International Crisis Group.
Speaking from his office in the Kyrgyz capital, Bishkek, he said: "The issue is purely financial. The country is falling to pieces. There is an energy crisis and people don't have enough electricity or jobs and it will get worse. The economy only just functions at best. The government will expect the US to make a counter-offer.
"Russia has tied its aid to the closure of the base but the ultimate decision will be made on the basis of money. Russia is putting the screws on the president. The US will now have to try to get him to change his mind and offer more money."
The question now is whether such an offer might not be too late.
The future of the base is an important test for President Obama. He plans to significantly increase the number of US forces in Afghanistan from its current level of 32,000. An interruption of the supply route would make that task much more difficult.
He also has to face the realities of Russian power in the region, as Russia appears to be gearing up to test American will and influence there.
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