A senior State Department official said Tuesday the president of Uzbekistan (search) made it clear that American forces must leave their air base in the Central Asian country, and the U.S. intends to do so "without further discussion."

The demand came as relations soured following U.S. criticism of Uzbekistan's crackdown on anti-government protesters in May in the eastern city of Andijan (search).

"The Uzbek government made it clear that we need to leave the base, and we intend to leave it without further discussion," Assistant Secretary of State Daniel Fried (search) told reporters after meeting with President Islam Karimov.

In July, the Uzbek government invoked a provision of the basing agreement with the United States that requires all American forces to leave within six months.

Fried said the United States will withdraw the base within the period demanded by the Uzbek authorities. "We respect the deadline," he said.

The former Soviet republic hosted the U.S. troops for operations in Afghanistan in the wake of the Sept. 11, 2001, terrorist attacks.

U.S. officials did not immediately provide the number of U.S. troops at the Uzbek base.

The United States intends to pay a nearly $23 million bill to Uzbekistan for use of the base for almost four years.

Fried said the sum "is not a price for the right to have a base, it is a payment for material services provided by the Uzbek side."

"The United States and Uzbekistan have had a very difficult period in relations complicated by grave concerns regarding the human rights situation and events in Andijan," Fried said.

He dismissed as "ludicrous and non-credible" the allegations made by defendants in the ongoing trial of 15 men suspected of involvement in the May 13 Andijan revolt that the U.S. Embassy in Tashkent provided money to those who plotted the rebellion.

"We are not to be accused of an intention to establish an Islamic caliphate in Uzbekistan," Fried said, referring to the Uzbek authorities' claim that the defendants had planned to establish an Islamic state.

Uzbek authorities hope the carefully choreographed trial will refute accusations that government troops fired on a crowd of protesters in Andijan, killing hundreds, and support its contention that extremist Islamic groups from abroad encouraged the protest.

Human rights groups allege that the confessions were coerced through torture.

"I made it clear we support civil society and NGOs around the world," Fried said, commenting on the recent shutdown of two American aid groups in Uzbekistan. "I regret NGOs are under pressure from the Uzbek government."

The uprising in Andijan began when militants seized a prison and freed 23 businessmen who were on trial for alleged Islamic extremism. The attackers also seized a local administration building and took hostages, as thousands of demonstrators gathered in an adjacent square to press economic and social grievances.

Human rights groups and refugees who fled to Kyrgyzstan claimed that the revolt led to a brutal government crackdown that killed more than 700 people, mostly civilians shot while trying to flee. The government said 187 people died, mostly militants.

Karimov, a hard-line autocrat, has ruled Uzbekistan since the Soviet era.