An explosion at a police station in the Russian town of Makhachkala near Chechnya may have caused casualties, police said.
The explosion happened at 2.20pm local time.
Makhachkala is capital of the region of Dagestan, which borders Chechnya and has been rocked by an overspill of fighting, with Islamists and police battling each other almost every day.
A bomb killed 10 soldiers in the town on Friday as they were on their way to a steam bathhouse. An Islamist militant group claimed responsibility for planting the device.