A string of suicide bombings struck three cities in Saudi Arabia on Monday in what looked like a rare coordinated series of attacks that marked the fourth set of terrorist offensives in less than a week that appear tohave been carried out by ISIS militants. Compared to the other attacks of the past week, these ones did not appear to have caused many casualties but were high in symbolic value. The deadliest attack took place near the Prophet’s Mosque in the city of Medina, which is considered the second-holiest city in Islam after Mecca. The bomber apparently detonated his explosives in the parking lot of the sprawling mosque after security officers raised suspicions about him. Four security officers were killed and five others were injured in the explosion.

The Medina attack that apparently took place close to a security station for the Prophet’s Mosque, where the Prophet Muhammad is buried, “shocked Muslims around the world, particularly as it happened on the penultimate day of Ramadan,” notes the National. “It was very shocking that such a thing happens in such a holy place for Muslims, the second holiest place in the world,” a 25-year-old Sudanese visitor to Medina told the Associated Press. “People never imagined that this could happen here.”

This picture is so symbolic. It's like a stab in the heart of every Muslim. #Medina @akhbar pic.twitter.com/L46glGVp79 — Jenan Moussa (@jenanmoussa) July 4, 2016

There was also an explosion near the U.S. consulate in Jeddah that injured two security officers and at least one bomber struck in the eastern city of Qatif near a Shiite mosque.

WATCH: Suicide bomb blast in the holy city of #Medina pic.twitter.com/EFcHFjK4i5 — Press TV (@PressTV) July 4, 2016

No one has claimed responsibility for the attacks, but the bombings appear to bear all the hallmarks of ISIS by targeting American citizens, Shiite worshippers, and Saudi security forces. Plus, ISIS has carried out attacks in Saudi Arabia in the past and see the country—and its monarchy—as a key target. And while there have been several attacks in Saudi Arabia in the past, multiple attacks on the same day are exceedingly rare. The seemingly coordinated attacks come after a bloody week in which there had already been deadly terrorist attacks in Turkey, Bangladesh and Iraq near the end of the holy month of Ramadan. That hardly seems to be a coincidence considering ISIS had specifically called on supporters to carry out attacks during Ramadan.

Although Monday’s attacks weren’t as deadly as they could have been they still “offered further evidence that in the three years since it declared the existence of its so-called caliphate, the Islamic State has developed the capacity to strike at will at the time of its choosing in diverse locations around the world,” notes the Washington Post.