The latest happened shortly after noon (5 a.m. ET) Friday outside the Imam Hussein mosque in Dammam, a coastal city about 70 kilometers (45 miles) from the Persian Gulf island nation of Bahrain, a Saudi source with detailed knowledge of the investigation said.
The attacker -- dressed in traditional female clothing as a cover-up -- had been challenged by Shiites who had volunteered to search those going into the mosque in the wake of the previous week's attack
the Imam Ali mosque in the village of Qudayh, according to the source.
The bomber then set off explosives -- killing himself and three Shiite worshipers, the source said.
In a statement, Wichita State University identified one victim as Abduljaleel Alarbash, 22, an undergraduate student in electrical engineering who had returned to Saudi Arabia to get married. He was to return to the university in the fall.
"The Wichita State University community is saddened by the tragic death of one of our students," the statement said. "Our condolences go out to Abduljaleel's family, friends and colleagues in this time of loss."
Alicia Newell, director of the university's engineering career center, told CNN affiliate KWCH that Alarbash made the "ultimate sacrifice" if he was among the volunteers who challenged the bomber.
"I think the way in which he passed away shows a lot about the person," she said. "He was definitely a pleasure to work with."
Saeed AlGhamdi, president of the the university's Saudi student association, said he knew Alarbash for three years.
"He was funny, a good guy and we are sorry (about) what happened to him," he said.
A Saudi Interior Ministry spokesman gave a slightly different account of the attack, saying "security authorities" went up to a suspicious vehicle as it was parking adjacent to the mosque, according to the official Saudi Press Agency.
"When the security men approached the car, it exploded, killing four people -- one of them believed to be the driver -- and spreading fire to a number of cars," the spokesman said.
Video shot inside the mosque
shows men sitting and looking forward at someone talking calmly in front of them. Then comes the sound of a large explosion, leading people to yell out in shock and start moving around.
Friday's carnage happened in the predominantly Shiite neighborhood of Anoud in Dammam, the capital of Saudi Arabia's oil-rich Eastern Province. It is one of the few Shiite population centers in a country in which 85% to 90% of citizens are Sunni, the other major Islamic sect.
ISIS claimed responsibility for the attack, according to a statement posted to Twitter by its supporters -- showing the terrorist group's efforts to bring violence and chaos to another Middle East country after its successes in Syria, Iraq and Libya.
"In a blessed martyrdom operation, a Polytheistic monument was targeted, that (the Shiite community) established in Sunni areas to spread out their polytheism," ISIS reportedly said, identifying the suicide bomber as Abu Jned al Zazrawi.
Fighting in Libya
ISIS claimed to have taken control of an airbase on the outskirts of the Libyan port city of Sirte, according to an online statement posted by the group on Twitter.
The group said its forces were engaged in heavy fighting for control of the city with militias.
Fighters from the Fajr Libya coalition retreated Thursday night from the base, which has an adjoining civilian airport, said Mohammed Shami, chief spokesman for the militia coalition, which calls itself the Libyan government after seizing control of Tripoli in 2014.
Air operations at the base and airport ceased several months ago, when fighting between ISIS and the militia started in the area, Shami said.
Only one nonoperational military aircraft was left on the base when the militia retreated.
The spokesman added that militia fighters are fighting ISIS forces on the perimeter of Sirte and have prevented them from entering the city.
Sirte is about 440 kilometers (273 miles) east-southeast of Tripoli.