WASHINGTON (CNN) -- After months of delay, the United States has established an embassy in Baghdad, the State Department said Monday.

Undersecretary for Management Patrick Kennedy said Monday he signed a "certificate of occupancy," which gives the United States ownership of the heavily fortified embassy compound inside the Green Zone and allows staff to move into its 27 buildings.

Kennedy said that before he approved final occupancy, he got assurances from a team of experts who tested the fire, electrical, mechanical and communications systems inside the buildings.

The sprawling facility will provide secure housing for U.S. personnel who currently live and work in Saddam Hussein's former Republican Palace, which has increasingly come under fire inside the Green Zone.

U.S. Ambassador Ryan Crocker told reporters Friday he expected officials to begin moving into the facility in late May or early June.

A recent spike in insurgent attacks that killed several Americans in the Green Zone prompted the State Department to order U.S. Embassy personnel not to leave reinforced buildings. A shortage of such space has forced some diplomats to temporarily sleep at the new embassy compound, despite the lack of occupancy certification.

"It's been a difficult few weeks, rockets are bouncing off your buildings, and maintaining focus can be an occasional challenge," Crocker said. "We worry a lot less about formal safety certifications and a lot more about ensuring people have a place to sleep where rockets couldn't get at them."

The Vatican-size compound, which will be the largest U.S. diplomatic facility in the world, was scheduled to open in September at a cost of $592 million, but the price tag is expected to rise to more than $730 million.

Completion delays, safety concerns and new requirements for additional secure office space for the U.S. ambassador and the commander of multinational forces in Iraq delayed the project by six months. The project started 2½ years ago.

Concerns over the fire detection systems also slowed completion of the embassy, and drew criticism from Congress.

CNN has reported on U.S. Embassy documents that detailed such problems in the complex as poor quality construction, faulty electrical wiring, malfunctioning fire systems and unacceptable formaldehyde fumes in some of the compound's buildings, which the U.S. government ordered repaired.

Congress also has voiced concern over charges of fraud against the main contractor, First Kuwait.

Based on congressional testimony, it is believed the U.S. Justice Department is conducting an investigation into the embassy project. E-mail to a friend

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