MOSCOW (Reuters) - Russian prosecutors said on Monday they suspected Kremlin critic Bill Browder of ordering the murder of a lawyer whose memory he has championed, but he dismissed the accusation as a cynical ploy to tar him for lobbying for sanctions on Moscow.

FILE PHOTO: Hermitage Capital CEO William Browder is sworn-in before a continuation of Senate Judiciary Committee hearing on alleged Russian meddling in the 2016 presidential election on Capitol Hill in Washington, U.S., July 27, 2017. REUTERS/Yuri Gripas/File Photo

Browder, the British head of investment fund Hermitage Capital Management, has led a campaign to expose corruption and punish Russian officials he blames for the 2009 death of Sergei Magnitsky, whom he had employed as a lawyer, in a Moscow jail.

The prosecutors said they had opened a new criminal investigation into Browder and vowed to seek his arrest for creating an international criminal group.

They accused U.S.-born Browder, 54, of setting up companies to launder millions of dollars and said they suspected he may have poisoned four former colleagues, including Magnitsky.

Nikolai Atmonyev, an aide to Russia’s prosecutor-general, said it was “highly likely” that Browder himself had ordered the poisoning of Magnitsky in jail, citing testimony from a former cellmate, RIA news agency reported.

Magnitsky was arrested in 2008 shortly after alleging that Russian officials were involved in large-scale tax fraud. He complained of mistreatment by the authorities before his death.

The accusations - which relate to crimes dating from more than nine years ago in at least one case - are the latest in a series to be directed at Browder. He has cast them as a vendetta waged by President Vladimir Putin for his lobbying, which in 2012 led to U.S. sanctions on Russia in the ‘Magnitsky Act’.

“I really struck a nerve with the Magnitsky Act,” Browder wrote on social media on Monday, describing the latest allegations against him as “Kafka-esque”.

“FEVER DREAM”

Browder drew a parallel between the accusations against him and the poisoning of former Russian spy Sergei Skripal and his daughter Yulia in England in March. The West blamed Russia for the poisoning, which caused a flurry of tit-for-tat diplomatic expulsions.

“Putin’s ‘fever dream’ response to being caught poisoning the Skripals is accusing me of four murders, including poisoning of Sergei Magnitsky,” Browder wrote on Twitter.

Last year a Russian court sentenced Browder in absentia to nine years in jail after finding him guilty of deliberate bankruptcy and tax evasion.

The U.S. sanctions imposed under the Magnitsky Act imposed visa bans and asset freezes on Russian officials linked to the death of Magnitsky.

Putin has dismissed allegations of foul play against Magnitsky and said he died of heart failure.