Updated

Moscow is grappling with a slew of fake bomb calls that have prompted the evacuation of shopping malls, schools, railway stations and administrative buildings.

The Tass news agency says there were over 100 anonymous bomb warnings in Moscow on Friday. No explosives have been found.

Friday's calls were the latest in a wave of fake bomb threats that have haunted Russia for a month, prompting evacuations of tens of thousands of people and incurring massive economic damages.

Alexander Bortnikov, the director of the Federal Security Service (FSB), the main KGB successor, said Thursday the agency had tracked down four people suspected of engineering the wave of hoaxes. Bortnikov said the suspects were Russians living abroad who had accomplices inside the country, but he wouldn't identify them or describe their motives.