Russian Ambassador to Britain Alexander Yakovenko has told the UK government that its report implicating President Putin in the 2006 murder of former spy Alexander Litvinenko is a "gross provocation of the British authorities".

"We consider the Litvinenko case and the way it was disposed of a provocation of the British authorities," he said.

The statement came after a British inquiry found that President Vladimir Putin probably approved a 2006 Russian intelligence operation to murder ex-KGB agent Alexander Litvinenko with radioactive polonium-210 in London.

"We will never accept anything arrived at in secret and based on the evidence not tested in the open court of law," said the ambassador. "This gross provocation of the British authorities cannot help hurting our bilateral relations. That was the conversation, the meeting was an exchange of views."

Litvinenko, 43, an outspoken critic of Putin who fled Russia for Britain six years to the day before he was poisoned, died after drinking green tea laced with the rare and very potent radioactive isotope at London's Millennium Hotel.

An inquiry led by senior British judge Robert Owen found that former KGB bodyguard Andrei Lugovoy and another Russian, Dmitry Kovtun, carried out the killing as part of an operation probably directed by Russia's Federal Security Service (FSB), the main heir to the Soviet-era KGB.