Sanjar Umarov was arrested more than three months ago

Sanjar Umarov, who leads the Sunshine Uzbekistan group, was held in 2005 for embezzlement - a charge his supporters deny and say is politically motivated.

He has been held incommunicado in one of Tashkent's prisons ever since his arrest in October.

Mr Umarov's lawyer said that when he visited his client in jail shortly after the arrest, he found him naked and incoherent.

Mr Umarov, an entrepreneur with business and family ties in the US, was accused of money-laundering and other economic crimes which relate to business dealings in Uzbekistan several years ago.

He came to prominence last year in the wake of May's shootings in the city of Andijan, where eyewitnesses say troops killed hundreds of people.

His group openly criticised the government's repressive policies and called for free-market reforms in Uzbekistan, where the economy has stagnated because of excessive centralisation and corruption, the BBC's Ian MacWilliam in Central Asia says.

'Drugged'

Mr Umarov was arrested shortly after sending a letter to parliament calling on lawmakers to discuss reforms.

His supporters allege that he has been drugged by the authorities.

Human rights groups say the Uzbek authorities often use mood-altering drugs to extract confessions - a claim that Tashkent denies.

Our correspondent says that since the shootings, the government has been rounding up anyone who openly criticises its policies.