ST. PETERSBURG, December 9. /TASS/. More than a dozen hospitals and several school in various areas across St. Petersburg received warnings about concealed explosives, an emergency source told TASS.

"About 11 St. Petersburg hospitals, as well as several schools and college prep educational centers in various city neighborhoods, received threats," the source said.

Earlier the joint press service of the St. Petersburg courts reported that on Monday the city’s courts were evacuated due to the bomb threats. They are now operating again and no dangerous objects were found.

According to earlier reports, an anonymous letter to the Primorsky District Court also warned about the threat of an imminent explosion at the Hermitage State Museum and at Pulkovo Airport. The Hermitage’s press service said that a security sweep found the premises clear of any suspicious objects, and Pulkovo told TASS that they hadn’t received any threats and that the airport is operating according to schedule.

This current wave of bomb threat messages began two weeks ago, with a bomb ransom e-mail being sent to the St. Petersburg City Court. The perpetrators demanded that 120 million rubles ($1.8 mln) be transferred in bitcoins to a digital wallet. Other city courts, ranging from district courts and to military ones, have received similar letters, along with shopping malls and schools. All of them have turned out to be false alarms.