An ISIS suicide bomber on Friday blew himself up at the entrance of a mosque in Eastern Province, killing three people, exactly seven days after the terrorist group attacked another mosque in the oil-rich region.

The so-called “Najd Province”, which claimed both bombings, defended attacks on Shiites and said they should be "killed everywhere", in an audio message posted online late Friday.

“The Islamic State has ordered its soldiers everywhere to kill the enemies of religion, especially the Rawafedh (Shiites)," a spokesman for the group is heard as saying in the audio message.

Shiites are "apostates" and "it is our duty to kill and displace them... wherever they may be," added the unidentified speaker.

3 people were killed and four others also wounded in Friday's attack in the city of Dammam, which coincided with weekly prayers.

The attack sparked wide condemnation.