BAGHDAD (AP) — U.S.-led coalition forces in Baghdad said Tuesday that attacks on coalition personnel and facilities in Iraq "will not be tolerated," adding that coalition forces retain the right to self-defense.

No coalition or U.S.-occupied facility was struck in Monday night's attack in which two Katyusha rockets were fired into the heavily fortified Green Zone, according to a statement issued by the coalition and Iraqi security forces.

The rockets landed few hundred meters (yards) away from the U.S. Embassy compound's perimeters, triggering alert sirens that sounded across the capital's Tigris River.

"We take this incident seriously as do our Iraqi security forces partners," the coalition statement said.

No side has claimed responsibility for the attack, which comes amid heightened tensions in the region following an attack on Saudi oil installations that the U.S. has blamed on Iran.

Similar attacks in the past have sometimes been blamed by Iraqi forces on Iranian-backed militias in Baghdad.

The militias have recently said they will retaliate to a series of airstrikes that have targeted their bases and weapons depots in recent weeks. No one has claimed the attacks but Israel, which frequently targets Iranian interests in neighboring Syria, is believed to be behind at least some of them. Some Iran-backed groups have publicly blamed Israel and its U.S. ally by extension.

A member of the Popular Mobilization Forces, the umbrella group for Iran-backed militias, said the forces fired the rockets at the Green Zone from the Dora district southwest of the capital. He spoke on condition of anonymity because he was not authorized to give this information.

A senior security official refrained from pointing fingers and said authorities were still investigating Tuesday night's rocket attack. Speaking on condition of anonymity in line with regulations, the official however said Iran-backed militias were likely to have fired the rockets considering they had vowed to retaliate to the airstrikes on their bases.

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