A truck packed with explosives crashed through the gates on Monday of the police headquarters in the southern Russian city of Nazran and exploded, killing at least 12 people, officials said.
In a statement, the Investigative Committee of the State Prosecutor's office said the attack occurred as police officers lined up for roll call at the start of their morning shift.
The statement said a small, Russian-made truck known as a "Gazelle" broke through the security gate at the headquarters and entered the territory of the building.
"A powerful explosion occurred after this," the statement said, adding that the apparent attack caused "significant damage" to the building itself and resulted in "a large number" of dead and wounded.
The Investigative Committee said in a separate statement posted on its website that 12 people were killed and 24 others wounded and taken to hospital as a result of the attack.
Victims were rushed to the main hospital in Nazran but Interfax news agency reported there were not enough beds to accommodate all of them.
"All of those injured are currently being treated," a local hospital worker told the news agency.
"Many of them are in serious condition. The exact numbers of dead and wounded are still being determined. At present at least 30 people have been brought to the hospital with injuries and traumas of varying degrees."
Nazran is the chief city in the restive southern Russian republic of Ingushetia that has been beset by attacks on law enforcement personnel by Islamist fighters.
The attack on the Nazran police station came four days after the Ingushetia president, Yunus-Bek Yevkurov, announced he was returning to his post despite still recovering from serious injuries sustained in a June 22 bomb attack.
Last Wednesday, the republic's construction minister, Ruslan Amerkhanov, was shot dead in a brazen attack inside his own office, fueling fears that the situation in Ingushetia, which neighbours Chechnya, is spinning out of control.
Moscow has long struggled to impose the Kremlin's authority in the volatile North Caucasus region, which has been the site of two full-fledged wars in Chechnya and hundreds or thousands of violent attacks since the 1991 collapse of the Soviet Union alone.