The arrest of a man whose publications have frequently criticised the policies of the Kremlin and Russian President Vladimir Putin, have brought angry reactions from several prominent Russians.

Rival Boris Berezovsky has criticised Gusinsky's arrest

"It's a piece of discrimination which discredits Russia," said Boris Nemtsov, a deputy speaker of parliament and senior member of the liberal Union of Right's Forces.

Boris Berezovsky, another powerful Russian media figure, said his "personal attitude to what has happened to Gusinsky is very negative, whether he's guilty or not".

Vladimir Gusinsky

1989: Entered the business world and founds the Most-Bank 1992: Began developing media empire, launching Russia's first independent TV station NTV 1994: Police raid the Most-Bank 1996: Backs Boris Yeltsin in Presidential elections 1999: Defects to the opposition with strong anti-Yeltsin campaign

President Putin said that Mr Gusinsky's detention had been a surprise for him and that he would look into the situation immediately.

Speaking during a visit to Spain, the president said he hoped the prosecutor-general's office had "enough grounds and that all was done within the law".

"I do not know anything about this. The prosecutor-general's office takes its decisions independently," he added.

Last month investigators backed by armed policemen raided Media-Most's offices, reinforcing criticism that President Putin intended to crack down on news outlets critical of his administration.

In the US, White House spokesman Joe Lockhart said: " We are quite concerned about some of the steps taken against the free media."

Harsh conditions

Sergei Parkhomenko, editor of the Gusinsky-owned "Itogi" weekly magazine, said that Gusinsky was being held in Moscow's 18th century Butyrsky jail, not the more modern Lefortovo prison where high-ranking detainees are usually held.

"It is the ugliest jail in Moscow, where only criminals are held," he said.

"They won't let us see him until tomorrow. They arrested him late in the day intentionally so they could tell us they are closed and keep him out of contact overnight," he added.