The troops have mainly been used to support military efforts in Afghanistan. There are now about 800 Americans in Uzbekistan and 1,200 in Kyrgyzstan. France also has air force personnel based in Tajikistan.
Now the SCO -- whose Central Asian members include those two countries, as well as Tajikistan and Kazakhstan -- says it is time for Washington to announce when it will withdraw those forces.
On 6 July in Bishkek, acting Kyrgyz Foreign Minister Roza Otunbaeva reiterated the call, saying the situation in Afghanistan was stable and that the Americans no longer needed the bases.
"All of us are part of the anti-terrorist coalition, including our country. However, there is a time limit for everybody who comes to stay somewhere," Otunbaeva said. "We are members of the Shanghai Cooperation Organization. We raised this issue [of the U.S. bases] together with the other [SCO] member states."
But Washington has rejected such calls. U.S. State Department spokesman Sean McCormack told a press briefing that it is up to individual states, not the SCO, to determine their relationship with foreign troops.
"Our presence and [that of other] countries -- some of the countries mentioned -- is determined by the terms of our bilateral agreements under which both countries have concluded that there's a benefit to both sides from our activities," McCormack said.
U.S. Defense Department spokesman Lawrence Di Rita said the bases are important for both the global war on terror as well as operations in Afghanistan.
Still, he said, the bases aren't crucial.
"There's been a great deal of assistance to important operations," Di Rita said. "But you know, we always have a range of options. And there's no one facility that is, you know, that is so critical that we couldn't manage without it."
Can the United States do without the bases, particularly the Khanabad base in Uzbekistan? And is the issue one of military logistics, or global politics?
James Phillips specializes in U.S. foreign policy and security issues at the Heritage Foundation, a private Washington policy-research center.
He says the United States has to be mindful of even the appearance of allying itself with an authoritarian leader like Uzbek President Islam Karimov after the bloodshed in Andijon in May.
But Philips told RFE/RL that the United States should be able to maintain operations in Central Asia, even at the Khanabad base in Uzbekistan.
"It [keeping U.S. forces at Khanabad] could be construed as a conflict of interest, but Washington did criticize the Andijon incident, and the Uzbek government retaliated by putting some restrictions on the use of the base," Philips said. "So I think the Bush administration made clear that it does not support such violent crackdowns, in contrast to both China and Russia, which supported the government crackdown there."
From a purely military standpoint, Phillips says the Uzbek and Kyrgyz bases are far more modern than the bases at Bagram and Kandahar in Afghanistan. More than two decades of war have left these bases less suitable for 21st-century airborne military missions.
Radek Sikorski disagrees. He is Poland's former deputy foreign and defense minister who now studies international affairs at the American Enterprise Institute, another Washington think tank.
He told RFE/RL he believes Central Asian bases are no longer essential -- but that severing military ties with Uzbekistan is:
"My judgment would be that we probably don't need it [Khanabad] so much as to censor ourselves in relations with what is clearly an authoritarian and nasty regime," Sikorski said. "My recommendation would be to withdraw the base if need be, rely on the bases that we have in a friendly country like Afghanistan itself, and tell Mr. Karimov to stuff himself and criticize him the way he deserves."
Sikorski says he believes a unilateral withdrawal would be better than simply submitting to the SCO demand for a timetable. He says he believes the demand was not generated independently by Uzbekistan and Kyrgyzstan, but was inspired by Russia and China who want to keep the Central Asian states outside the U.S. sphere of influence.
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