By Sarah Shenker BBC News

Russia and China fear the US presence undermines its influence

Speaking to US troops in Kyrgyzstan, Secretary Donald Rumsfeld seemed pleased that the US had won assurances that it could continue to use an airbase in this Central Asian republic.

Many believed that the US position in the former Soviet republic was not really in jeopardy.

Yet Mr Rumsfeld's trip was said to be in direct response to regional pressure on the US to withdraw.

Earlier this month, the Central Asian states, backed by Russia and China, called on the US to give a timeframe for withdrawal of forces.

Mr Rumsfeld's visit - his second this year - highlights how important and sensitive the US presence is in the region.

'Power politics'

About 1,000 troops are stationed at Manas International Airport near the Kyrgyz capital, Bishkek. The US also makes use of the Karshi-Khanabad airbase in Uzbekistan.

It has no troops based in Tajikistan or Kazakhstan, but it has an arrangement to refuel aircraft in Tajik airfields and to fly over Tajik territory.

With the nearest bases as far away as Turkey and South Korea, the Central Asian bases play an essential role in supporting military operations in Afghanistan.

The lack of a base in the region before 2001 delayed the start of US operations in Afghanistan and possibly played a part in allowing Osama Bin Laden to evade capture, says Svante Cornell, deputy director of the Central Asia-Caucasus Institute at Johns Hopkins University.

But as well as the clear military advantage, the bases also allow the US to monitor developments in the region.

"The US is interested in Central Asia because it is a significant land mass that could become a haven for terrorists," Mr Cornell told the BBC News website.

"There is a lack of central government control in many regions. Groups with links to al-Qaeda have operated in the region. The drug trade out of Afghanistan is also a factor in regional instability."

He says that objections to the US presence have been fuelled by Russia and China, which view Central Asia as their sphere of influence.

"This is old-fashioned power politics," Mr Cornell says. "They believe that a US presence decreases their influence.

"The more conservative elements in those countries would say that they feel that the US is trying to encircle them to prevent them having their rightful role in the region."

US criticism

While not setting a date for withdrawal, Kyrgyzstan's defence minister said after meeting Mr Rumsfeld that US forces would have no reason to stay on once the situation in Afghanistan stabilised.

However, analysts believe the bases could remain longer.

The US base at Manas contributes about $50m (�28.7m) a year to the Kyrgyz economy, according to US officials - a considerable sum in a country where the average annual wage is just $330.

Operations in Afghanistan show no signs of winding down

"Also, from a military perspective, I think the US will seek to retain their bases, to have the potential to address threats that arise quickly," Mr Cornell says.

The future of the US base in Uzbekistan is less secure.

Flights into Karshi-Khanabad were reduced at the request of the Uzbek authorities, after the US criticised the government over its violent put-down of an uprising in Andijan in May.

"Uzbekistan sees itself as a regional power and it feels that the US has let it down by criticising it," Mr Cornell says.

"The Bush administration's emphasis on human rights and democratisation has given Russia and China the chance to increase the gap between the Central Asian states and the West. They can say, 'We don't ask you tough questions, we will help you be safe and it's no problem if you don't have elections'."

Russia and China will continue to exert pressure on Kyrgyzstan and Uzbekistan, Mr Cornell says, but with limited success for the time being.