The Foreign Ministry accused Britain of "paranoid spymania" on Wednesday and hinted that the arrest of a Russian aide to a member of parliament could set back efforts to improve relations with London.
The Ministry attacked the handling of the case of Yekaterina Zatuliveter, 25, an aide to a Liberal Democrat on the British parliament's defense committee. The Sunday Times reported this month that she was suspected of espionage.
In a statement, the ministry said Zatuliveter had been released on bail and that Russia had been told that she was accused of violating only immigration law, but added that there was "no clarity" from British authorities.
Her arrest spawned a "bacchanalia of conjecture about 'evil deeds' … against the United Kingdom," the ministry said.
It likened the situation to the "theater of the absurd" and said it was fueled by "paranoid spymania manifesting itself just as a dawn started to emerge in Russian-British relations."
Russia and Britain have sought to mend ties damaged by the 2006 killing in London of Kremlin critic Alexander Litvinenko with a rare radioactive isotope. Russia refuses to extradite a State Duma deputy whom Britain wants to try for the killing.
On Wednesday, President Dmitry Medvedev praised the efficiency of the Foreign Intelligence Service in a year dominated by the deportation of a group of Russian agents from the United States.
"This year … was a difficult one for the Foreign Intelligence Service," Medvedev said at a ceremony marking the 90th anniversary of the agency. "Nevertheless, I think our service remains capable of resolving tasks in a quick … and, more important, efficient way."
His remarks suggested there would be no major repercussions for the head of the agency, former Prime Minister Mikhail Fradkov, despite the summer scandal that led to the biggest spy swap since the Cold War.
Russia traded four people accused of spying for the West in return for 10 Russian agents living in the United States, including the flame-haired Anna Chapman.
Their arrests were widely seen as an embarrassing failure for Russian intelligence and prompted speculation Fradkov would be dismissed. But the Kremlin has cast the incident in a softer light, praising the agents and awarding them high state honors.
Medvedev warned the intelligence service to guard against the kind of breaches that led to publication of U.S. diplomatic cables by the website WikiLeaks, which portrayed Russia as a corrupt nation and Medvedev as Prime Minister Vladimir Putin's junior partner.
The leaks were "good in a way" because they showed "how potential competitors see you," he said. "But no one is insured against leaks, and we should keep that in mind for the future."
Earlier this month, Medvedev said the cables revealed the cynicism of U.S. diplomacy but suggested they would not significantly harm improving ties with Washington.