The widow of murdered dissident Alexander Litvinenko has praised Gordon Brown for "standing firm" in his discussions with the new Russian president.
In a strongly-worded statement, Marina Litvinenko criticised the Russian government, who she said may have been complicit in her husband's murder.
Mr Brown failed to thaw relations with Moscow after he held face-to-face crunch talks with Dmitry Medvedev at the G8 summit in Japan.
Ex-Russian agent Mr Litvinenko died in a London hospital on 23 November 2006 from radiation poisoning.
Andrei Lugovoy, a former associate of Mr Litvinenko, is believed to be a main suspect in the dissident's murder.
It is understood that Russia's refusal to extradite Mr Lugovoy was discussed during the talks in Japan.
Mrs Litvinenko said: "I am convinced that the harassment of the British Council and British Petroleum in Moscow were devised by the Kremlin to induce Britain to stop pursuing Mr Lugovoy's extradition.
"I was relieved to find out that the Prime Minister stood firm and explained to Mr Medvedev that there can be no compromise on that."
She added: "Britain once again has shown that it would not short change its principles in the face of bullying and blackmail. I am proud of being British.
"I hoped that President Medvedev would tell the truth about my husband's murder; by doing so he would distance himself from the previous regime. It appears that he chose to side with it. The difference between him and Mr Putin is only in style but not in substance."
