People watch the U.S. flag as it is raised during a ceremony marking the opening of the new U.S. Embassy in Baghdad, Iraq, Monday, Jan. 5, 2009. The embassy in Baghdad is one of the largest U.S. embassies in the world.

Baghdad ? The United States inaugurated its largest embassy ever on Monday, a fortress-like compound in the heart of the Green Zone — and the most visible sign of what U.S. officials call a new chapter in relations between America and a more sovereign Iraq.

U.S. Marines raised the American flag over the adobe-colored buildings, which sit on a 104-acre site and has space for 1,000 employees — more than 10 times the size of any other American Embassy in the world.

“Iraq is in a new era and so is the Iraqi-U.S. relationship,” Ambassador Ryan Crocker proclaimed.

In perhaps an unintended sign of the new relationship, Prime Minister Nouri al-Maliki did not attend Monday’s ceremony because he was traveling in Iran, a country the U.S. has accused of aiding and arming Iraqi militants.

Explaining the opening of such a large embassy three years before the U.S. must finish withdrawing its 146,000 troops from Iraq, Crocker told The Associated Press that it is vital for the U.S. to remain involved in nonmilitary ways.

“I think we have seen a tremendous amount of progress,” Crocker said before the ceremony, “but the development of this new Iraq is going to be a very long time in the making, and we need to be engaged here.”

Crocker said Baghdad was looking to the West for the first time since the Army’s 1958 revolution that toppled Iraq’s monarchy and set the stage for the ascendance of the Baath party, which dominated Iraq until the 2003 invasion.

The inauguration of the $700 million embassy came just days after a security agreement between Iraq and the United States took effect, replacing a U.N. mandate that gave legal authority to the U.S. and other foreign troops to operate in Iraq.

Under the new security agreement, U.S. troops will no longer conduct unilateral operations and will act only in concert with Iraqi forces. They must also leave major Iraqi cities by June and the entire country by the end of 2011. Another accord mapped out the bilateral relations.