The first, in November 2014, was a gun attack. And, in May 2015, there have been two devastating suicide bomb blasts targeting worshippers at Friday prayers.
The last two attacks used RDX, a powerful military explosive, and have been claimed by IS's self-styled Najd Province, named after Saudi Arabia's staunchly conservative Sunni heartland, the desert plateau in the middle of the country.
So what is IS trying to achieve and will it succeed?
These attacks are a watershed for Saudi Arabia.
How it reacts now and in the coming months will determine whether the largest and most important Arab state can stave off a wider sectarian conflict between the country's majority Sunni and minority Shia Muslim populations, something that would be disastrous for both communities.
The attacks follow decades of state and religious discrimination against the Shia minority, who constitute about 10% of the population. » | Frank Gardner, BBC security correspondent | Thursday, June 04, 2015
