The director of the U.S. Central Intelligence Agency, John Brennan, says the three bomb attacks in Saudi Arabia last week bore the "hallmark" of the Islamic State group.
No one has claimed responsibility for the attacks, but Brennan told an audience Wednesday in Washington, "Those three attacks were, I think, the work of ISIL," using the U.S. government's preferred abbreviation for Islamic State.
"ISIL presents a very, very serious threat, not just to Europe and the United States ... but inside of Saudi Arabia," he said at the Brookings Institution.
A suicide bomber in the holy city of Medina detonated explosives July 4 at a checkpoint outside one of Islam's holiest sites, the Prophet's Mosque. Hours later, the Saudi Interior Ministry said, four security officers were killed and five others were wounded as they moved to prevent the attacker from entering the facility.
The mosque — the second holiest site in Islam — is the burial site of the Prophet Muhammad, who died in 632 AD. It is visited by millions of Muslims from across the globe each year during pilgrimages to Mecca.
Two other explosions were reported in the kingdom as the holy month of Ramadan drew to a close.
Several days after the attacks, the Saudi government announced the arrests of 19 suspects, including 12 Pakistanis.
In the past year, Saudi authorities have increased the arrests of radical Islamists. The nation's top cleric, Sheikh Abdulaziz al-Sheikh, has declared the IS group to be an "enemy of Islam."