LONDON, April 29 (Xinhua) - Britain's Foreign, Commonwealth and Development Office on Wednesday announced the revocation of the accreditation of a Russian diplomat, in response to Russia's expulsion of a British diplomat last month.

A British government spokesperson said London strongly condemned Moscow's "unjustified decision" to expel the British diplomat, as well as the "malicious public smear campaign" that followed.

"This behavior is wholly unacceptable, and we will not tolerate harassment or intimidation of our diplomatic staff," the spokesperson said.

"Any further action by Russia will be treated as an escalation and met with a firm and proportionate response," the spokesperson added.

Russia's Federal Security Service said on March 30 that it had revoked the accreditation of a British diplomat over "intelligence and subversive activities." The diplomat, identified as Janse Van Rensburg, a second secretary at the British Embassy, was ordered to leave the country within two weeks. ■