At least 28 people have been killed and 25 injured in a twin suicide bombing at Iraq's interior ministry, police say.
The roads around the ministry were quickly sealed off by police
Shortly before, there were conflicting reports of a mortar landing near a parade being held to mark the 84th anniversary of Iraq's police force.
The interior and defence ministers and the US ambassador were watching the parade at the police academy, but were said to be unhurt.
Al-Qaeda in Iraq claimed the blast in an unverified internet posting.
The statement said the attack was "to avenge the Sunnis who were subjected to all sorts of torture at the prisons of this ministry".
Sunni groups in Iraq have claimed that abuse is common in Shia-run prisons under the interior ministry's control. The ministry has strongly denied the claims.
Police said two bombers - at least one of whom was wearing a police uniform - had entered the interior ministry compound through a security checkpoint to the rear.
Guards shot one of the men because he looked suspicious, causing his explosives belt to detonate.
The second bomber, who had not been spotted, blew himself up minutes later as police and security officials gathered at the site of the blast.
State television said that, moments earlier, a mortar bomb landed in the grounds where the annual Iraq Police Day parade was being held a few metres away.
But this report was rejected by US military spokesman Lieutenant-Colonel Barry Johnson, who was at the ceremony.
"The blast could be heard in the distance, but no mortar hit the parade ground," he told Reuters.
Later reports suggest a mortar shell may have landed several hundred metres away, causing limited damage.
The event was being shown live on television and was attended by Interior Minister Bayan Jabr, Defence Minister Saadun al-Dulaimi and US ambassador Zalmay Khalilzad.
The interior minister gave orders that the procession should continue.
Election probe delay
The latest violence came as electoral officials announced there would be a delay in the publication of its findings into fraud allegations in the 15 December elections.
"There are still four to five small outstanding items," Abdul Hussein al-Hindawi of the Iraqi electoral commission told the AFP news agency.
He said he expected the findings to be announced after the four-day Eid al-Adha feast, which is due to begin this week.
A group of foreign monitors are also completing a separate probe. The International Mission for Iraqi Elections has spent the last week observing how the commission conducted vote counting and handling complaints.