Russia has accused "influential forces" in the UK of trying to sabotage relations between the two countries.
Responding to the arrest and detention of alleged spy Ekaterina Zatuliveter, the Russian foreign ministry urged Britain to prove with "concrete acts" its commitment to improving co-operation between London and Moscow.
Miss Zatuliveter, 25, is facing deportation from the UK amid suspicions that she used her position as an assistant to MP Mike Hancock to pass documents to Russian intelligence.
Russian diplomats have been pressing for information from the Foreign Office and Home Office about why she is being held.
In a sign of Moscow's anger at her treatment in the UK, the Russian foreign ministry said in a statement: "As for the eagerness with which some media in the UK are trying to stage a vaudeville about the worn-out spy plot, this cannot fail to awaken pity.
"We have no illusions that in Britain there are and will be highly influential forces, who are not interested in the normalisation of Russian-British relations.
"We hope, however, that the London Government's stated policy of improving bilateral co-operation will be reinforced by concrete acts."
Alexander Sternik, Russia's charge d'affaires in the UK, claimed that Britain had so far failed to provide information about the charges against Miss Zatuliveter.
Known as Katia, she has protested her innocence and says she is confident she will win an appeal against her deportation.
Her father, Andrei Zatuliveter, also criticised her treatment. "I always thought that England was a democratic country. People cannot be detained for no reason," he told the BBC.
