The suspects in the Salisbury Novichok attack should be “brought to justice”, Theresa May has said ahead of a meeting with Russian President Vladimir Putin.
The PM told the BBC Russia needs to stop its “destabilising activities”.
The UK believes two officers from Russia’s military intelligence service, the GRU, were behind the poisoning of former spy Sergei Skripal and his daughter Yulia in March 2018.
The Kremlin has denied any involvement in the case.
Mr Skripal and his daughter both survived the poisoning but last July a British woman, Dawn Sturgess, died after coming into contact with Novichok through handling a contaminated perfume bottle.
Scotland Yard and the CPS say there is sufficient evidence to charge two Russians – who go by the names of Alexander Petrov and Ruslan Boshirov – for attempted murder.
The meeting on the margins of the G20 summit in Osaka, Japan, is the first formal bilateral meeting between the two leaders since the 2018 attack.
Speaking to BBC deputy political editor John Pienaar, Mrs May said the poisoning was a “despicable and irresponsible act”.
“We have been clear, we’ve set out the evidence, charges have been made against two Russian individuals,” she said.
“Russia does not allow the extradition of its nationals but European arrest warrants are out for those two individuals and if they set foot outside Russia we will be making every effort that they are brought to justice.”
“Russia needs to recognise its acts and stop acting in this way and stop its other destabilising activities around the world, including for example its use of disinformation and cyberattacks,” she added.
In an interview with the Financial Times, Mr Putin said he hoped “a few preliminary steps” would be made towards restoring relations between Russia and the UK.
However, he appeared to have little sympathy for Mr Skripal, a former Russian military intelligence colonel who was jailed after being accused of spying for Britain before being released as part of a spy swap.
“Treason is the gravest crime possible and traitors must be punished,” Mr Putin told the newspaper.
“I am not saying that the Salisbury incident is the way to do it. Not at all. But traitors must be punished.”