Multiple bomb hoaxes caused up to 45,000 people to be evacuated from major buildings and transport hubs in cities across Russia, local media reported.
In Moscow, 30,000 citizens were cleared from train stations, shopping centres and a university in response to simultaneous anonymous phone calls on Wednesday.
Senior government officials gave no explanation for the threats.
President Vladimir Putin's spokesman, Dmitry Peskov, declined to comment on the calls.
Earlier, an emergency services official told news agency Tass: “This appears to be a case of telephone terrorism, but we have to check the credibility of these messages."
They said the calls began at the same time and continued after the evacuations began.
Tass reported three stations, Leningrad, Kiev and Kazan were evacuated, as well as the Moscow State Medical University, along with more than a dozen shopping centres including GUM, located on the iconic Red Square, facing the Kremlin.
Specialist officers with sniffer dogs were seen investigating the buildings. No explosives were found.
Associated Press contributed to this report
