Anonymous callers reported bombs on board at least three passenger planes flying out of Moscow on Thursday, but all three of the jets safely reached their destinations in other parts of the country.

The latest bomb threats come after several other Russian planes were also targeted by hoax bomb threats earlier this week. Moscow police received unconfirmed reports of 600 bombs planted in the city on Tuesday alone, including all 232 Moscow subway stations, 80 bridges, 15 courts, and 200 malls.

"The evacuation effort was minimal, some 1,500 people," said a source cited by the Russian Interfax news agency. "Not a single threat was confirmed."

Russia has been facing waves of false bomb reports since 2017, with President Vladimir Putin dubbing the phenomenon "telephone terrorism" in September that year. However, Russia's security forces and intelligence agencies were unable to track down those responsible.

In late January 2020, Russia's communications watchdog Roskomnadzor and its FSB security service blocked two encrypted email services, ProtonMail and StartMail. The Russian authorities believe anonymous users were using the services to send out bomb threats.

Some of the messages containing bomb threats refer to pro-Kremlin billionaire Konstantin Malofeyev, according to Russia's Meduza news website. The anonymous messages demand that he returns 120 bitcoins (some $743,500 €696,800 at Thursday's rates) in cryptocurrency that he allegedly stole from the now-defunct cryptocurrency exchange system in 2018. Malofeyev has denied any wrongdoing.

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