The government of the central Asian state shut down foreign broadcasts and tightened security at important buildings in an attempt to stop the unrest in the eastern valley from spreading.

Neighbouring Tajikistan, Kyrgyzstan and Kazakhstan – which all share part of the restive valley – closed their borders as the tide of popular discontent sweeping through the former Soviet region flared into violence.

Yesterday’s clashes in Andijan were sparked by the arrest of 23 Muslim businessmen, facing what human rights organisations claimed were trumped-up charges of religious extremism.

The defendants, who were freed in a storming of the Andijan jail, were accused of having links to the outlawed Hizb-ut-Tahrir party.

This radical Islamist group, whose purported heartland is in the Ferghana valley, is accused of mounting attacks in Uzbekistan that killed more than 50 people last year, allegations the group denies.

Yevgeny Primakov, a former Russian prime minister, told Interfax news agency: “The events in the Ferghana valley pose a great danger to stability in the region. It is critical not to allow a split between the north and the south of Uzbekistan.”

Uzbek authorities have been displaying more signs of nervousness and intolerance. They cracked down on media and dissidents after Georgia’s “rose revolution” in 2003 that ousted President Eduard Shevardnadze. Many foreign non-governmental organisations were banned.

Up to 6,000 political dissidents are in jail, and the government, suspicious of both religious groups and business, has closed down private enterprises.

Allison Gill, Human Rights Watch’s representative in Tashkent, said protests had arisen more often owing to economic issues and government interference than in response to political or religious grievances.

She said the 23 men arrested in Andijan were subscribers to the Akramiya religious ideology. The movement gives Muslims a set of rules for life – including requirements to strive for success and give tithes to the poor.

“Akramism is compromised mostly of successful businessmen – like the 23 in jail,” Ms Gill said, adding that rights monitors were aware of 50 arrests over suspected links to Akramism this year.

Protests about the trial began 10 days ago when the men’s employees gave out leaflets. “It looks like last night the employees whose jobs were threatened went to free the defendants.”

She doubted that much of Uzbekistan would learn of the unrest but said she would not be surprised if it spread to other towns. Uzbekistan’s poor human rights record has received little publicity since the US recruited the country as an ally in its “war on terror” in October 2001 – setting up a military base in the southern town of Khanabad to aid operations in neighbouring Afghanistan.

Hundreds of millions of dollars of aid flowed in, with critics accusing the US of turning a blind eye to the torture record of the regime of the president, Islam Karimov.

The White House last night urged restraint but added that some of the prisoners who had been freed were from a “terrorist organisation”. They did not elaborate, and the US embassy in Tashent could not say who they were referring to.

“We don’t know who they are talking about,” said Ms Gill. “The use of the word terrorist is unjustified and plays into Uzbek government policy by justifying torture by calling it anti-terrorist measures.”

One leading critic of the abuses, the former British ambassador to Tashkent Craig Murray, highlighted a case in which one prisoner was apparently boiled alive.

Mr Murray believes that his publicising of the abuses eventually cost him his job. He said that the unrest would spread, but it would take time. Of the news blackout, he said: “I have spoken to three people in Tashkent who have no idea about Andijan.”