Berlin (CNN) The widow of Alexander Litvinenko has urged the UK government to do more to protect Russians who have sought shelter in Britain following the attempted assassination of former Russian spy Sergei Skripal and his daughter Yulia.

The UK government has not yet said who is behind the nerve agent attack on Skripal and his daughter in the southern English city of Salisbury, but speculation is rife that Moscow could be responsible.

A British inquiry found that two Russian agents poisoned Alexander Litvinenko at a London hotel bar in 2006 by spiking his tea with highly radioactive polonium-210. From his deathbed, he insisted that Russian President Vladimir Putin and the Kremlin were responsible for what happened.

Alexander Litvinenko is pictured in a London hospital on November 20, 2006, three days before his death.

His widow, Marina Litvinenko, told CNN in an exclusive interview Thursday that it was too early to jump to conclusions in the Skripal case. But she acknowledged she had immediately seen "similarity of a way to assassinate" between this attack and the case of her husband, whom she refers to as Sasha.

Speaking in Berlin, Litvinenko said some lessons had been learned -- but that more should have been done by the UK government. As well as expelling Russian intelligence operatives from British soil, the authorities should "prevent people who have been involved in crime in Russia who have all this dirty money to bring and use this dirty money in the UK," she said.

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