A suicide car bomb blast killed 18 people, including 10 police, in the northern city of Kirkuk on Tuesday, and mortars landed near the US ambassador to Iraq during a ceremony in Saddam Hussein's hometown of Tikrit.
The bomber detonated his explosives-laden car next to a group of police vehicles on the main road leading south from Kirkuk to Baghdad shortly after sunset. Police Colonel Borhan Tayyib Taha said 28 people were wounded in the blast.
Ambulances ferried the worst cases to hospitals in Kirkuk, where distraught relatives gathered to search for loved ones.
Police said they expected the toll to rise as many of those injured were badly wounded.
Kirkuk is a mixed Arab, Kurdish and Turkmen city that has seen frequent episodes of violence, some the result of tensions between the separate communities, all of whom claim ownership of the city, which lies close to vast oil reserves.
Today's attack came hours after insurgents fired two mortars at a complex of palaces built by Saddam in Tikrit, where US Ambassador Zalmay Khalilzad was attending a ceremony handing the palaces back to the Iraqi government.
No one was injured by the blasts, which the US military said failed to detonate properly, but television pictures showed US soldiers and Marines, as well as Khalilzad and other dignitaries, diving for cover during a panicked few seconds.
General George Casey, the top US commander in Iraq, was also attending the ceremony.
"This is a phenomenon existing in the country. We are used to it," Khalilzad told reporters after security guards had rushed him to a safer place and then brought him back.