The United States is trying to increase the flow of non-lethal supplies to US troops in Afghanistan via Uzbekistan as it may not always be able to count on the Pakistan route, a US official said Saturday.

The official spoke as US Secretary of State Hillary Clinton visited Tajikistan and Uzbekistan, part of the US military's Northern Distribution Network (NDN), following a trip to Pakistan to discuss troubled ties there.

"As a general rule, we're trying to get more (goods) through Central Asia and through Uzbekistan," the senior State Department official, who was accompanying Clinton, told reporters on condition of anonymity.

"We've always said that we prefer to use the Pakistan route because it's cheaper, it's shorter," the official said, recalling that the northern route goes via the Baltic states, Russia and Kazakhstan.

"But still, it's (the northern route) a good thing to have," he added.

"And again with our (often troubled) relations with Pakistan, we always have to be prepared should they decide to either want to restrict our access or, even in the worst case, close it off," the official said.

"We would be prepared to move north through Central Asia if necessary," he said.

The route from Uzbekistan is a rail link that distributes fuel and other non-lethal goods. He said about 50 percent of surface shipments take that route.

The Uzbeks however are "sensitive" about publicising the route to Afghanistan for fear that it will prompt "retribution" from the Taliban and other Islamist militants in the region, he added.

In February 2009, during improving relations with Washington, Uzbek President Islam Karimov said he would allow the United States to transport non-military supplies through his country as part of the NDN.

In 2005, Tashkent closed the US air base in the country which was used to support US troops in Afghanistan after US criticism of a bloody crackdown on unrest in Andijan in the country's east.

The US official said there were no plans to hold negotiations to reopen the base. Nor were there plans, he said, to increase supplies through Tajikistan, which is a small supply route.

Clinton visited Islamabad on Thursday and Friday to urge Pakistan to dismantle havens in Pakistan that militants use to launch attacks in neighboring Afghanistan, an issue that has put a heavy strain on US-Pakistani ties.