Uzbekistan—President Islam Karimov of Uzbekistan has blamed Islamic militants for violent clashes that reportedly left up to 500 people killed when troops opened fire on protestors in the eastern city of Andijan.

Addressing the nation, the autocratic leader of the former Soviet republic said the riots had been plotted by outside forces and foreign extremists, and he mentioned a group called Hizb ut-Tahrir al-Islami (Islamic Party of Liberation).

On Friday, armed supporters of 23 jailed Muslim businessmen stormed state buildings in the city of 300,000 people, freeing some 2,000 prisoners. In response, police and soldiers fired on the protesters, who were calling on Karimov to resign.

Wire services say that up to 500 bodies were laid out at a school in the city.

Violence spread beyond the city, with clashes reported between troops and gunmen near the border with Kyrgyzstan. Local residents in a border town seized control of government offices, setting some alight.

Karimov defended the crackdown and said the unrest was organized by an offshoot of Hizb ut-Tahrir.

“They are brainwashing young people with ideas of creating a unified Islamic state,” he said. “Their aim is to unite the Muslims and establish a caliphate.”

If allegations of Hizb-ut-Tahrir’s involvement in the riots are confirmed, it would mark the first time the group has been implicated directly in a terrorist attack.

With supporters in many parts of Europe and Asia, the group claims to be nonviolent, but does not deny its ultimate goal of replacing existing political regimes with theocratic dictatorships under Islamic law (a caliphate, or Khalifah in Arabic).

The group, whose secretive structure is said by experts to emulate Marxist-Leninist organizational principles, expanded into Central Asia at the time the Soviet Union was collapsing in the early 1990s.

In the authoritarian post-Soviet states in Central Asia, Hizb ut-Tahrir has spread its influence. Regional media report successes in penetrating parliament in Kyrgyzstan, the media in Kazakhstan, and customs offices in Uzbekistan.

The movement has large followings in the “stans,” and in Uzbekistan alone at least 500 members are behind bars.

Regional security officials have warned that efforts are underway to unify radical Islamic groups in Central Asia, including Hizb ut-Tahrir, Uighur separatists from neighboring western China, the Islamic Movement of Uzbekistan (IMU) and possibly Chechen separatists.

Activities in recent years have included an alleged assassination attempt against Karimov, which was blamed on the IMU.

Russian President Vladimir Putin, a supporter of Karimov, discussed the situation in a telephone call with him at the weekend and expressed “serious concern” over possible destabilization in Central Asia.

We are receiving disquieting information that everything that happened there was pre-planned,” Russian Foreign Minister Sergei Lavrov said Sunday.

“According to our information, the group that had prepared all this and tried to bring it to fruition included various representatives, including the Taliban,” Lavrov said, in reference to the radical militia that ruled most of neighboring Afghanistan until toppled by U.S.-led forces in late 2001.

Moscow has banned Hizb-ut-Tahrir and extradited some suspects to Central Asia.

For Islamic militants, Uzbekistan has become an obvious target because the country has been a strong supporter of U.S.-led campaign in Afghanistan.

American troops are using a former Soviet air base in the south of Uzbekistan to support operations against the remnants of the Taliban.

White House spokesman Scott McClellan urged the government in Tashkent and the demonstrators to “exercise restraint at this time.”

“The people of Uzbekistan want to see a more representative and democratic government, but that should come through peaceful means, not through violence,” he said.

State Department spokesman Richard Boucher said Friday the U.S. had been “very clear about the human rights situation” in Uzbekistan, and urged calm.

Human rights campaigners say the Karimov government has arrested and jailed thousands of people accused of extremism or fundamentalism.