WASHINGTON (AP)  U.S. diplomats will begin moving into the mammoth new, heavily fortified embassy in Baghdad next month after long delays in the $736 million project — and not a moment too soon. Increasing rocket attacks on the Green Zone have killed four Americans in recent weeks and have embassy staff wearing body armor and ducking for cover. U.S. Ambassador to Iraq Ryan Crocker said Friday that construction is complete at the Vatican-sized compound and that although not all buildings have yet been certified for final occupancy, transition to the facility from the less-protected location in a Saddam Hussein-era palace should start at the end of May. "It's been a difficult few weeks, rockets are bouncing off your buildings, and maintaining focus can be an occasional challenge," Crocker said, referring to the recent spate of insurgent attacks in the Green Zone that have killed at least two U.S. soldiers and two American civilians. "We will begin moving into the new embassy — some of the office space and the apartments — probably the end of next month, the beginning of June, so that will certainly improve quality of life and provide some added protection," he told reporters. The rise in insurgent attacks prompted the embassy late last month to order personnel not to leave reinforced buildings and to wear helmets and body armor if they must go outside. A shortage of space in fortified areas has forced some diplomats to sleep at the new embassy site despite the lack of occupancy approvals. "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," said Crocker, who has served in battle zones before, notably in Lebanon during its civil war in the 1980s. "Being under attack is a lot like being under attack, whether it is in Lebanon or Iraq," he said. "The incoming sounds about the same and has about the same impact." The new embassy will be the largest U.S. diplomatic mission in the world, with fortified working space for 1,000 people and living quarters for several hundred on a 104-acre site. But the project has been beset by construction, logistical and security hitches that caused major delays beyond its planned September 2007 opening date and angered some lawmakers. In October, the department conceded that a host of problems, including major malfunctions in the complex's physical plant, including electrical and water distribution systems, would push back the embassy opening at least until this spring. Some of those problems have since recurred. Some of the deficiencies have been blamed on shoddy work by the company hired to build the project, First Kuwaiti General Trading & Contracting Co., for $592 million. Changes to the original design have pushed the cost up by $144 million. First Kuwaiti has been accused of tricking foreign laborers into working on the embassy, mistreating them, and paying $200,000 in kickbacks in return for two unrelated Army contracts in Iraq. The company denies the charges. Congressional Democrats have launched investigations into whether the State Department had adequate control of the project, which has been complicated by security concerns, including a September incident in which private Blackwater USA guards are accused of killing 17 Iraqi civilians while protecting an embassy convoy. In his comments on Friday, Crocker defended the work of private security contractors like Blackwater as "absolutely essential" to the functioning of embassy staff. The State Department last week renewed Blackwater's contract despite the fact that an FBI investigation into the September incident is still underway. Crocker said he and his team would not able to do their jobs if they did not have such protection. "The challenges of getting the nation's business done in Iraq are pretty substantial," he said. "We have to function in conditions that would in most places have us pretty much in a stand-down. But this is the nation's most critical work, and it has to go on, and security contractors like Blackwater are absolutely essential to this effort." Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more