Jan. 16 (Bloomberg) -- Russia's Federal Security Service, the main successor to the KGB, said it will investigate Russian staff employed at U.K. cultural offices, raising pressure in a dispute between the two countries.

The FSB agency said today it will interview Russian citizens working for the British Council to prevent them from being used as an ``instrument in provocative games'' of the British authorities.

The Russian Foreign Ministry said Jan. 14 it would stop issuing visas for U.K. diplomats who work with the British Council outside Moscow after Britain refused to close its cultural activities in Yekaterinburg and St. Petersburg. It also threatened to take action against the cultural body's main office in the Russian capital.

The confrontation threatens to further sour relations between Russia and the U.K., which have sunk to a post-Cold War low since the 2006 murder in London of dissident ex-Russian agent Alexander Litvinenko.

The FSB, in a statement released through Russian news agencies and confirmed over the phone by its press service, said it was acting after the U.K. ``ignored'' Russia's lawful demands. The British Council could not immediately be reached for comment.

U.K. Foreign Secretary David Miliband said yesterday Russia's retaliatory measures ``can only make matters worse'' in relations between the two countries.

Miliband said the U.K. government would respond to Russia ``shortly'' in the British Council dispute after consulting with its ``international partners.''

Colonial Era `Nostalgia'

Russian Foreign Minister Sergei Lavrov retorted that Britain was demonstrating ``nostalgia for the colonial era'' and this was ``not the right language for talking to Russia.''

Russia last month ordered the U.K.'s cultural promotion body to close its regional offices by Jan. 1.

The British Council defied the order, reopening its branch in St. Petersburg on Jan. 14 and in Yekaterinburg on Jan. 9 after the Russian New Year holidays. Its two British employees in St. Petersburg have diplomatic status, while local staff run the Yekaterinburg office.

Russia has linked its closure of the British Council offices to the dispute over the Russian refusal to hand over ex- KGB bodyguard Andrei Lugovoi, whom U.K. prosecutors want to put on trial for the November 2006 lethal radiation poisoning in London of Litvinenko. The Russian constitution forbids extradition.

The U.K. in July expelled four Russian diplomats, triggering a tit-for-tat response, and froze cooperation with the FSB.

To contact the reporter on this story: Henry Meyer in Moscow at Hmeyer4@bloomberg.net.

Last Updated: January 16, 2008 03:03 EST