Russia ordered the expulsion of the United Kingdom's defence attache in Moscow on Thursday, a move it said was direct retaliation for London expelling Russia's defence attache last week.
The UK had accused Moscow's defence attache -- a diplomat in charge of military affairs -- of being "an undeclared military intelligence officer", a charge Moscow called a lie.
"The defence attache at the British Embassy in Moscow, A. T. Coghill, has been declared persona non grata. He must leave the territory of the Russian Federation within a week," it said.
The ministry warned it could take further measures in response to the UK's decision, which it called "unfriendly", "anti-Russian" and politically motivated.
UK defence minister Grant Shapps called Russia's expulsion of Coghill "a desperate move".
"Whilst Russia's DA in the UK was acting as a spy, Putin's only issue with ours was that they personified the UK's unwavering support for Ukraine," Shapps said.
Russia's defence attache, Maxim Elovik, was thought to have been in the UK since at least 2014 and has been pictured at wreath-laying ceremonies commemorating Russian war dead.
Relations remain tense between Russia and the UK, which is a staunch NATO backer of Ukraine and has provided Kyiv's troops with significant military support.
{{/usCountry}}Relations remain tense between Russia and the UK, which is a staunch NATO backer of Ukraine and has provided Kyiv's troops with significant military support.
{{/usCountry}}The UK said it made the decision amid concerns of "malign" Russian activity on British soil, including an arson attack on a Ukrainian-linked business allegedly orchestrated by the Kremlin.