RIYADH, Saudi Arabia—The leader of an attack that killed eight people in a small Shiite village this month was connected to Islamic State militants, the government said, as it announced the arrest of 77 people it linked to the assault.

The government said the leader, whom it identified as Abdullah bin Saeed Al Sarhan, received orders from abroad “specifying the target, the targeted, time of execution” of the attack in the oil-rich Al Ahsa region in the east, where many of the kingdom’s Shiite minority reside.

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