Sergei Lavrov told Russian media the expulsions would “definitely” happen.
The announcement follows suit with the UK, with Prime Minister Theresa May having confirmed yesterday that 23 Russian envoys would be made to leave Britain within a week.
Mrs May also revoked an invitation to Russia’s foreign minister and said the Royal family would not attend the FIFA World Cup in Russia later this year.
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 Salisbury.
Moscow has denied any responsibility.
The allegations by Mrs May have been labelled “insane” by Russia’s foreign ministry.
When asked when the expulsions would happen, Mr Lavrov was quoted as saying: “Absolutely. Soon. I promise you that.”
He reportedly referred to the UK allegations against Russia as “absolutely boorish”.
Mr Lavrov has linked Britain’s reaction to the spy poisoning affair to Brexit.
He said the UK’s approach to the matter was partly prompted by the Government’s problems over negotiating its way out of the European Union.