MOSCOW, September 19. /TASS/. More than 20,000 people were evacuated on Tuesday from some 30 buildings in Moscow and three other Russian regions, namely the Moscow and Rostov regions and the Yamal-Nenets autonomous area, over bomb calls, a source in law enforcement agencies said.

"There were 27 bomb calls. Anonymous callers warned about comb threats at ten administrative buildings, 14 shopping malls, two hotels and one school," the source said, adding that all the buildings were inspected by specialists with dogs.

"Some calls have proved to be hoax, others are still being examined," the source added.

A wave of bomb calls in Russian cities began on September 11. The peak of such calls was reported on September 13 when anonymous callers warned of possible explosions at 100 facilities, mostly schools, railway terminals, airports and trade centers, in Moscow only.

According to TASS sources, the police believe it was a planned action organized by a group of persons. The mass media offered various theories, from the so-called Ukrainian trace (like in 2014, when false bomb calls came from Ukrainian telephone numbers) to a theory that Islamic State is behind these bomb threats.

A TASS source said that the police were taking effort to identify the hoax callers.