Berezovsky has been a frequent Kremlin critic

The adverts have appeared in leading papers in the UK and the US, including the Financial Times, Daily Telegraph, Washington Post and New York Times.

The Russians, led by UK-based tycoon Boris Berezovsky, launch a tirade of accusations against Mr Putin. They portray him as a genocidal president who has flattened democracy and has allowed Nazi-era techniques to be used to whip up public feeling.

Mr Bush, please use this chance - look into the eyes of your friend again Russians' advert

The campaign, costing an estimated �250,000 ($410,000), is addressed to US President George W Bush, who has described Mr Putin as an "honest, straightforward man".

It raises seven questions about Mr Putin's conduct in the Kremlin,accusing him of:

• bringing Russia's parliament, media and courts under virtual Kremlin control and turning elections into a farce
• committing war crimes and genocide in Chechnya
• placing his former KGB allies into more than 50% of key government positions
• presiding over a society which now lives in fear.

The advert also alleges that Russian secret services are exploiting anti-Semitism and xenophobia in order to "demonise" big business and create "militaristic hysteria similar to Germany under the early Nazi regime".

SIGNATORIES Boris Berezovsky - tycoon granted UK asylum Elena Bonner - widow of Andrei Sakharov Vladimir Bukovsky - Soviet-era dissident Ruslan Khasbulatov - Chechen intellectual and politician Ivan Rybkin - leader of Liberal Russia

"Friendship is built on shared values," the advert says. "Mr Bush, please use this chance - look into the eyes of your friend again."

Mr Putin leaves on Tuesday for a visit to the US which will include talks with Mr Bush.

The Russian embassy in London would not comment on any of the allegations. The US embassy said the White House would become aware of the advert because of its prominence in the US press.

Political asylum

Although the advert is issued in the name of the little-known Foundation for Civil Liberties in New York, the campaign is believed to have been handled from London, where Mr Berezovsky is now based.

He was granted political asylum in the UK earlier this month.

The advertisement appeared in leading papers in the US and UK

Another of the five Russian signatories, former political prisoner Vladimir Bukovsky, also lives in the UK after defecting during the Soviet era.

The three others are still based in Russia - dissident Andrei Sakharov's widow Elena Bonner, and two former chairmen of the Russian parliament Ruslan Khasbulatov and Ivan Rybkin.

Mr Berezovsky is among the Russian "oligarchs" who made their fortunes in the chaotic years after the fall of communism.

But after Mr Putin replaced Boris Yeltsin in the Kremlin, the oligarchs fell out of favour and a number have been accused of fraud and other criminal offences.

Campaign costs

Mr Berezovsky's friend and fellow oligarch Roman Abramovich has become the owner of Chelsea football club in the UK.

Although expensive, the campaign is not expected to have stretched the billionaire tycoon Mr Berezovsky financially.

A full promiment page in the FT's worldwide edition would normally cost more than �80,000.

In the New York Times, the cost is more than $100,000 (�80,000) and in the Washington Post the page would have cost around $94,000 (�57,000).