An Islamic State affiliate that calls itself Najd Province said it was behind a deadly bombing at a Shiite mosque on Friday in Kuwait City, the third in a string of attacks that the previously unknown group has claimed responsibility for in wealthy Saudi Arabia and Kuwait.

Here's a look at the attacks on Shiite mosques that the group, which calls itself Najd Province -- a reference to the historic region of the central Arabian Peninsula where the Saudi capital Riyadh is located -- claims was its work:

   May 22

A suicide bomber unleashed a blast in a Shiite mosque in eastern Saudi Arabia as worshippers commemorated the birth of a revered saint, killing 21 people and wounding dozens more. The attack happened in the village of al-Qudeeh in the eastern Qatif region, the heartland of Saudi Arabia's Shiite Muslim minority.

It was the deadliest militant assault in the kingdom in more than a decade.

The Islamic State group views Shiites as apostates deserving of death and also seeks the overthrow of the Saudi monarchy, which it considers corrupt and illegitimate. Islamic State leader Abu Bakr al-Baghdadi has repeatedly called for attacks on the Saudi kingdom.

Following the attack, the Islamic State warned of more "black days" for Shiites in Saudi Arabia, a member of the U.S.-led coalition targeting the group.

   May 29

A suicide bomber disguised as a woman blew himself up in the parking lot of the only Shiite mosque in the Saudi port city of Dammam, killing four people. Dammam is in the kingdom's oil-rich east, where the Shiite community has long complained of discrimination.

The death toll at the Imam Hussein mosque could have been higher had authorities and worshippers not been on alert for attacks. One witness said the bomber was chased from the entrance away by young men who had set up checkpoints.

   June 26

An explosion at the Imam Sadiq Mosque in Kuwait City left at least 16 dead and dozens wounded. Following the attack in al-Sawabir, a residential and shopping district, a posting on a Twitter account known to belong to the Islamic State group said the attack was carried out by a suicide bomber wearing an explosive belt. IS said on Twitter that the bomber had targeted a "temple of the apostates."

All of the attacks took place on a Friday, when mosques are generally full of worshippers. The attacks bolster concerns that Islamic State militants are establishing a toehold outside of the group's stronghold in Iraq and Syria.