The UK is claiming that Russian President Vladimir Putin gave the order to assassinate the former intelligence agent Alexander Litvinenko.
According to the UK government, an investigation found that Litvinenko was poisoned with the radioactive isotope Polonium-210 in 2006. The poison was delivered to his tea by a former KGB agent and businessman who invited Litvinenko to an expensive hotel bar in London.
Russia has rejected the report and a Kremlin spokesperson said that "these sham investigations can only muddy the waters between the two countries."