A female suicide bomber blew herself up in the southern Russian region of Dagestan on Saturday, injuring at least 18 people, including two children and five police officers, authorities said. The attacker was later identified as a widow of two Islamist radicals killed by security forces.

It was the first suicide bombing in Dagestan since the Boston Marathon attacks last month. The brothers suspected of carrying out those blasts are ethnic Chechens who lived in this turbulent Caucasus province before moving to the United States. Tamerlan Tsarnaev, the elder brother who was killed in a shootout with police days after the April 15 bombings, spent six months in Dagestan last year.

Dagestan remains an epicenter of violence in the confrontation between Islamist radicals and federal forces. Islamist extremists are striving to create an independent Muslim state, or “emirate,” in the Caucasus and parts of southern Russia with a sizable Muslim population.

In Saturday’s attack, the bomber detonated an explosives-laden belt in the central square of the provincial capital, Makhachkala, said a Dagestan police spokesman, Vyacheslav Gasanov.

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

Police investigators work at a blast site outside a building used by court bailiffs in central Makhachkala on May 20, 2013. (Stringer/AFP/Getty Images)