A view of a site where two bombs exploded, in Makhachkala May 4, 2012. As many as 20 people were killed and 30 more wounded when two powerful blasts hit a police post outside the capital of Russia's violence-plagued Dagestan region. Reuters

A suicide bomb went off Saturday in the Russian city of Makhachkala, the regional capital of the Dagestan region in Russia’s North Caucasus, injuring at least 18 and leaving two police officers in critical condition.

The explosion occurred just off a tree-lined central thoroughfare near a building of the Russian Interior Affairs Ministry, according to Russian media outlet RT. The woman who detonated the bomb has been identified as Madina Alieva, 25. She had been twice widowed -- her first husband was killed in 2009, the other in 2012. Both were Islamists.

In Dagestan, it is not uncommon for women who lose husbands or relatives to perpetrate suicide attacks. The perpetrators are referred to as ‘black widows,’ and dozens have carried out similarly violent acts since 2000.

The North Caucasus, a majority Muslim region, is home to an Islamist insurgency that has grown increasingly violent in recent years -- especially after a separatist movement in Chechnya was defeated by Russia in 2000. Moscow’s counterinsurgency forces did not vacate Chechnya until 2009. Today, militant attacks occur sporadically across the region.

The North Caucasus garnered worldwide attention on April 15 after two ethnic Chechens, Dzhokhar Tsarnaev and Tamerlan Tsarnaev, detonated explosives that killed three people and wounded hundreds more at the finish line of the Boston Marathon.

The most recent terrorist attack in the Caucasus was on May 20, also in Makhachkala, when two bombs detonated near a court building, wounding scores of people and killing four.

Though no fatalities have yet been reported following Saturday’s attack, the explosion was strong enough to send shock waves. RT reports that the blast had a force equivalent to 500 grams of TNT.

While security officials continue their investigation in Makhachkala, victims and witnesses of the explosion in Boston have gathered with thousands of supporters to run the final mile of the Boston Marathon that was interrupted last month by the bombing.

Tamerlan Tsarnaev, who was killed during a clash with police shortly after the Boston bombing, spent several months in Dagestan in 2012. His brother, Dzhokhar, is currently in police custody.