BAGHDAD — Two suicide bombers detonated explosives-laden backpacks Thursday inside the heavily barricaded Green Zone, killing at least six civilians — including four Americans — in the first suicide attacks within the area that houses the offices of the interim Iraqi government and the U.S. and British embassies.

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The suicide bombings were the most deadly attacks inside the U.S.-controlled Green Zone, a 4-square-mile compound surrounded by blast walls, concertina wire and armed checkpoints.

Home to thousands of American soldiers, diplomats, contractors and Iraqi employees, the Green Zone was designed to serve as a safe haven for Westerners in Iraq. Many of its residents don't venture outside the protected compound.