Islamic State (IS) militants were quick to claim responsibility
for a suicide bombing at a packed Shiite mosque in Saudi
Arabia’s Eastern Province on 22 May that killed 21 people
and injured many more. It was the worst terrorist attack inside
the kingdom since 2004 (see From the archive, page 13), and the
first attack there to be claimed by IS, whose local branch issued
a statement warning Shiites of “black days” ahead.