A coordinated attack involving a suicide bombing on a open-air election campaign meeting north of Baghdad killed at least 22 people, officials said, two weeks before provincial polls.
A man on Saturday had thrown a grenade on the meeting in the restive city of Baquba, 60 km from the Iraqi capital, before a suicide bomber blew himself up, a police colonel and a medic at the city hospital said.
At least 60 people were wounded in the attack.
The meeting, held in a tent around lunchtime, was for campaign workers who supported Muthanna Ahmed Abdulwahid, a Sunni Arab candidate for the Azimun Ala al-Bina (Determined to Build) list, a small local party.
Abdulwahid was not harmed in the attack, officials said.
Iraq has been plagued by violence against election candidates ahead of provincial council polls due April 20, with 12 hopefuls already killed in the run-up to the vote, according to an AFP tally.
The polls will be the first in Iraq since 2010, and come after the withdrawal of US forces at the end of 2011.
Diyala province, of which Baquba is the capital, is among Iraq's most violent.
At least 560 people were killed there last year, according to Britain-based NGO Iraq Body Count, which said it suffered the highest per capita rate of civilian deaths in the country.
Diplomats have also raised concerns over a government decision to postpone elections in two provinces which, combined with the fact that four were never slated to vote, means that just 12 of Iraq's 18 provinces will cast ballots.
Also on Saturday, a civilian was killed and two anti-Qaeda militiamen were wounded in a bomb blast northwest of Baghdad, and security forces found the body of a policeman who had been kidnapped near the capital a day earlier.
Violence has spiked markedly ahead of the provincial elections, with 271 people killed in March, the highest such figure since August.