MOSCOW: Twelve people were hospitalised and two of them were in a critical condition after a female suicide bomber blew herself up in Russia's restive Dagestan region Saturday, in the second bombing attack this week, a police spokeswoman said.

The bomber blew herself up not far from the interior ministry building in the centre of Makhachkala, spokeswoman Fatina Ubaidatova told AFP.

The Moscow-based Investigative Committee said an unidentified woman came up to traffic policemen and detonated an explosive.

All the injured were hospitalised. Five were policemen and two of them were in a “critical condition”, Ubaidatova said.

The suicide bomber herself died. State television broadcast a picture of a young woman, her head covered with a scarf, suggesting she might have been behind the bombing.

Since 2000, at least two dozen women, most of them from the Caucasus, have carried out suicide bombings in Russian cities and aboard trains and planes.

All were linked to an Islamic insurgency that spread throughout Dagestan and the predominantly Muslim Caucasus region after two separatist wars in neighboring Chechnya.

The bombers are often called ''black widows'' in Russia because many are the widows, or other relatives, of militants killed by security forces.

The Tsarnaev brothers suspected of carrying out last month's Boston marathon bombings, are ethnic Chechens who lived in Dagestan before moving to the United States.

Tamerlan Tsarnaev, who was killed in a shootout with police days after the April 15 bombings, spent six months in Dagestan in 2012.

Dagestan remains an epicentre of violence in the confrontation between radical Islamists and federal forces.

This week, a double explosion in Makhachkala killed four civilians and left 44 injured, while three security officers and three suspected militants have been killed in other incidents

Human rights groups accuse security agencies of abductions, torture and extrajudicial killings of civilians that further fuel the confrontation with Islamic radicals.