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.
U.S. Ambassador Zalmay Khalilzad and top Iraqi officials were attending a nearby ceremony, but they were unhurt by the 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.
A U.S. newspape, Christian Science Monitor said gunmen in Baghdad kidnapped one of its reporters, Jill Carroll and killed her interpreter on Saturday.
And Iraqi election officials said they were delaying the release of vote results until after the Muslim holiday of Eid al-Adha this month.