Two suicide bombers disguised as Iraqi policemen blew themselves up during a ceremony at the Interior Ministry, killing at least 28 people Monday.
Officials said the bombers had police uniforms and security passes allowing them to access the highly-guarded site in Baghdad.
A mortar shell was also fired at the ceremony, which was attended by U.S. Ambassador Zalmay Khalilzad and Iraq's defense and interior ministers. No one was hurt by the mortar attack.
Al-Qaida in Iraq claimed responsibility. In an unverified statement, the group said the attack was a response to alleged abuse against Iraqi detainees in Interior Ministry custody.
Meanwhile, Iraqi election officials said they were delaying the release of vote results until after the Muslim holiday of Eid al-Adha this month.
And officials said Iraq's oil minister, Ibrahim Bahr al-Ulum, has returned to work, about a week after saying he would resign.
Meanwhile, U.S. military officials are investigating the crash of a Blackhawk helicopter that killed all 12 Americans on board near Tal Afar late Saturday. Elsewhere, insurgents killed three American Marines Sunday in Fallujah.
Some information for this report provided by AFP and Reuters.