The woman was identified as Madina Alieva, 25, who married an Islamist who was killed in 2009 and then married another Islamist who was gunned down last year, police spokeswoman Fatina Ubaidatova said.

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 Islamist 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. Islamist militants are thought to convince these widows that a suicide bombing will reunite them with their dead relatives beyond the grave.

Police said two of the people injured in the attack were in critical condition. There were no details about the injured children.

In the past week, a double explosion in Makhachkala killed four civilians and injured 44, while three security officers and three suspected militants were killed in other incidents. One of the devices was in a parked car, and the other was placed in a trash bin.

Although Chechen separatists were defeated almost a decade ago, Islamists continue to move through the region’s mountains and forests with comparative ease despite security sweeps by federal forces and police under the control of local leaders loyal to the Kremlin.

Human rights groups say that abductions, torture and extrajudicial killings of young men suspected of militant links by Russian security forces have helped swell the ranks of the rebels. Experts on the Caucasus say that Islamists routinely extort money from government officials and businessmen and attack or kill those who refuse to pay.

— Associated Press