Russian Foreign Minister Sergei Lavrov says the poisoning of Sergei Skripal could have been in Britain's interests.
The Kremlin has denied responsibility over the escalation of a diplomatic row between Russia and the West over the poisoning of the former spy in Salisbury.
In a news conference on Monday, Mr Lavrov accused western countries of "playing children's games" and hinted of the possibility of Britain being behind Mr Skripal's poisoning.
"There are other explanations besides those put forward by our Western colleagues who declare that it can only be the Russians who are responsible," he said.
"Experts say that it could be highly advantageous to the British security services as well, who are well known for their capacity to act with a licence to kill.
"It could also be advantageous to the British government, who clearly find themselves in a difficult situation, having failed to fulfil their promises to voters over Brexit.
"In times of cold war there were some rules, but now Britain and the United States had dropped all propriety."
Former double agent Sergei Skripal and his daughter Yulia are still in hospital after being poisoned by deadly nerve agent novichok on 4 March.
Russia has said it "insists" on seeing Ms Skripal after her condition dramatically improved. She is now understood to be conscious and talking.
The UK government - which claims the Russian state is behind the attempted murders - is looking into the legality of the request and also considering "the rights and wishes" of the 33-year-old.
Mr Skripal remains seriously ill and unresponsive.
Earlier on Monday, the Russian embassy accused Britain of flouting diplomatic convention by blocking access to the poisoned spy and barring it from the investigation into a murdered Russian businessman.
Hitting out at the Government, Russia's UK embassy tweeted a picture from zombie film 28 Days Later, complete with its biohazard logo.
Its message said: "28 days passed since the poisoning of Sergei & Yulia Skripal. UK hasn't complied with its obligation under the consular convention to provide access to the Russian citizens and the course of investigation."
As tit-for-tat expulsions continue, the first Russian diplomats to be kicked out of the US arrived back in Moscow on Sunday.
America has expelled 60 Russians, joining many European countries which also asked diplomats to leave in solidarity with the UK.
Russia continues to strongly deny any involvement and has responded to the West by throwing out an equal number of diplomats.
It has also published 14 questions about the investigation into the poisonings.
