The Uzbekistan visit by the commander of US forces in Afghanistan and Iraq, said State Department spokesman Gordon Duguid, "is not about supply routes or ... to the Manas air base in Kyrgyzstan."

Asked about the purpose of Petraeus’ top-level meetings Tuesday in Tashkent, Duguid at his daily press briefing referred reporters to the Pentagon.

"I am unaware that we are raising anything about supply routes (to Afghanistan) with Uzbekistan," he added.

Duguid further reminded reporters the Kyrgyz government had not officially notified Washington about its decision to close the Manas airbase near its capital Bishkek.

The Kyrgyz government announced earlier this month that it had decided to close the base, set up in 2001 to provide logistical support to the international coalition deployed against the Taliban and Al-Qaeda insurgents in Afghanistan.

The announcement came after Russia offered more than US$2 billion in aid to the impoverished Central Asian state in a region that a re-emboldened Moscow sees as its sphere of political influence.

The Kyrgyz government has insisted that Moscow did not set the closure of Manas as a condition for the aid.

The decision to close the Manas airbase is coming up for a vote in the Kyrgyz parliament possibly on Thursday, said the head of parliament’s foreign affairs committee that already approved the measure.

US President Barack Obama has authorized the deployment of 12,000 additional US troops to Afghanistan in the coming months, a US defense official said Tuesday.

The present 36,000-strong US force in Afghanistan has relied heavily on the Manas airbase for logistical support and Uzbekistan’s extensive rail system that links it to Afghanistan.

Defense Secretary Robert Gates a week ago said the Manas airbase was important "but not irreplaceable," adding: "We are looking at alternatives."

Petraeus flew to Uzbekistan overnight from Qatar, the US embassy there said, and will be leaving Taskhent to return to the United States later Tuesday after discussions are concluded.