Alexander Litvinenko
Marina Litvinenko (R), widow of Alexander Litvinenko, and her son Anatoly arrive at the Royal Courts of Justice Getty

The widow of Alexander Litvinenko has called for targeted sanctions against Vladimir Putin, saying it would be unthinkable for UK Prime Minister David Cameron not to take action after an inquiry found the Russian President probably approved the murder of her husband on British soil.

Marina Litvinenko said she was "very pleased" at the result of the inquiry, which found strong evidence suggesting Litvinenko was poisoned to death on the orders of Russia's intelligence agency, the FSB, in an operation approved by its then chief, Nikolai Patrushev, and the Kremlin.

After the inquiry report into the death of her husband was published, Litvinenko addressed Cameron: "I am calling immediately for the expulsion from the UK of all Russian intelligence operatives, whether from the FSB or other Russian agencies based in the London Embassy."

"I am also calling for the imposition of targeted economic sanctions and travel bans against named individuals, including Mr Patrushev and Mr Putin. It is unthinkable that the prime minister would do nothing in the face of the damning findings of [inquiry chairman] Sir Robert Owen," said Marina Litvinenko.

Alexander Litvinenko, a former Russian secret service agent who had received asylum in the UK, died after being poisoned with Polonium-210 in London in November 2006.

Marina Litvinenko's barrister Ben Emmerson told a press conference that due to the high radioactivity of the substance used, public health and security were also put at risk by the killers. "There were more than 100 individuals who were potentially contaminated and 200 sites in London where contamination traces were found. This is an issue of public health; an issue of danger in the streets.

"It would be surprising if the prime minister, who prides himself with keeping the streets of London safe from terrorism, would sit on his hands in the face of judicial findings not just of nuclear terrorism but of state-sponsored nuclear terrorism," said Emmerson.

The inquiry concluded that the two main suspects in the case, Andrei Lugovoi and Dmitry Kovtun, "probably" poisoned Litvinenko by lacing his tea at a the Millennium Hotel in Mayfair. The pair weren't present during the six-month hearings as Russia has refused to extradite them. Both men deny any involvement in murder.

According to the report, in the years following Litvinenko's death in 2006, Putin actively "supported and protected" Lugovoi, and also handed him an honour for services to the fatherland while the inquiry was taking place.

Marina Litvinenko said she was positive the killers of her husband will one day pay for their crimes. "Yes, they are walking the streets of Moscow today but I believe there will be a final day when these two people will be punished," she said.

The case has far-reaching diplomatic implications, with Russia playing a key role both in the crisis in Ukraine and Syria. Many analysts are doubtful the British government will take strong measures against Putin.

After the report was published swift action has been taken instead against Lugovoi and Kovtun. Interpol notices and European arrest warrants have been issued for the two suspects and the British Treasury has confirmed an asset freeze targeting the pair, while as the government considers further action.