Russia will expel UK diplomats "soon", said its foreign minister on Thursday, in response to the expulsion of 23 of its diplomats by Britain.
Sergei Lavrov told Russian media the expulsions would "definitely" happen, according to BBC.
The UK took its action after Moscow refused to explain how a Russian-made nerve agent was used on a former spy and his daughter in the UK.
Russia denies it was involved. Its foreign ministry called the allegations by Prime Minister Theresa May "insane".
Russia described the UK's position as irresponsible and not backed up by evidence.
When asked when the expulsions would happen, Mr Lavrov was quoted as saying: "Soon. I promise you that."
He reportedly referred to the UK allegations against Russia as "absolutely boorish".
Mr Lavrov also said the UK's approach to the matter was partly prompted by the government's problems over Brexit.