A number of organizations in the Russian city of Magnitogorsk have received anonymous e-mails warning of possible terrorist acts, local media have reported.
Hospitals, schools, and shopping centers were among the institutions that received the e-mails on January 21.
Local officials urged residents "not to give in to provocations by panicking."
Investigators were looking into the e-mails.
"Information about bombs purportedly planted at Magnitogorsk institutions is being verified," the press service of the Federal Security Service (FSB) said.
Police with canine teams were reportedly checking for explosives at local schools and hospitals, but none have been found. There were conflicting reports about whether some schools had been evacuated.
The FSB did not comment on the reports.
The city -- 1,400 kilometers southeast of Moscow -- has been on alert since December 31 when an explosion brought down part of a residential block, killing 39 people.
Authorities believe the blast was caused by a natural-gas leak and have rejected a claim of responsibility by the Islamic State terrorist organization.
Three people were killed in the city on January 1 when a van exploded.
Some Russian media sites have reported that the apartment building was targeted with explosives by three purported radical Islamists.
According to these unconfirmed reports, the three men were killed on January 1 near the site of the blast as they tried to break out of a police cordon in a minibus.
At the time, police said an exploding gas canister inside the vehicle caused it to burst into flames.
Several deadly apartment-building explosions in Russia in the past 25 years have been blamed on militants from the North Caucasus.
Household gas blasts have also been blamed for many such disasters.