The UK has been accused of "putting all decency aside" by Russia's foreign minister, over its claims Moscow is to blame for the poisoning of former spy Sergei Skripal and his daughter.
Sergei Lavrov appeared to suggest that UK secret services might have been involved in the attack in Salisbury, which he claimed could have been "beneficial" to the UK Government as a distraction from Brexit.
He added that it was "outrageous" Britain had failed to provide consular access to Yulia Skripal, since it emerged that her condition was improving.
The Russian Embassy in London has also issued a series of "questions without answer" about the poisoning, such as whether the UK has ever produced the Novichok nerve agent before, as it is believed this was used in the incident.
The UK has said that Russian state involvement is the only plausible explanation for the attack, and has led a worldwide reaction involving the expulsion of more than 100 diplomats.
However, according to Russian news agency Tass, Lavrov said Western countries are "playing children's games."
He added: "Today, our Western partners, and I first of all refer to the Great Britain, the United States and some other countries, which are blindly guided by them, put all of their decency aside and resort to bold lies and fake news."
Lavrov claimed Skripal had previously been "pardoned" and Moscow "could not have a possible motive" to attack him.
But he suggested the attack "can be also beneficial to the British Government which found itself in an inconvenient situation after failing to fulfil its promises to voters on Brexit's conditions."
Lavrov also said: "I consider this is outrageous that so far our multiple requests demanding access to our citizens have been rejected or have remained unanswered."
The UK has previously dismissed a series of Russian comments about the possible explanation for the poisoning as efforts to distract attention from Moscow's own failure to explain its part in the events.