A string of suicide attacks against Iraqi security forces killed at least 37 people, including 28 when two bombers blew themselves up among recruits at an army base.
The two bombers, one of whom wore an Iraqi military uniform, detonated explosives-filled vests at a recruitment centre on the Al-Saad base, east of the Diyala provincial capital of Baquba, a security official said.
At least 55 people were also wounded in the morning attack, which came ahead of a promised Iraqi army offensive in the province, an Al-Qaeda stronghold just north of Baghdad.
"We were about 30 people standing at the entrance," said one of the wounded, Falah Ali Hussein, 17. "They had just called our names when suddenly there was a big explosion."
A police officer said the victims were from a first batch of men called from across the province to participate in a military recruitment drive.
The US military said 20 Iraqi army recruits were killed and 55 wounded. The base has a joint Iraq-US security post but the American military said there were no US casualties.
Victims were ferried in ambulances and police vans to the nearby hospital in Baquba where relatives rushed to find loved ones.
Pictures taken by an AFP photographer at the hospital showed the wounded being treated in the lobby which was quickly covered with blood as dozens of victims were brought in.
Outside, a police officer was seen crying next to the body of his slain younger brother, while television footage showed several women searching among the bodies to identify sons who had gone to the military base.
Diyala and its capital Baquba are among the most dangerous areas in Iraq with frequent suicide attacks, including several by female assailants, as well as car bombings.
"Very soon there will be a big operation by our security forces in Diyala," interior ministry spokesman Major General Abul Karim Khalaf told reporters on Sunday without giving a specific timeframe.
In January, Iraqi and US troops launched "Operation Iron Harvest" in Diyala aimed at pushing Al-Qaeda out of long-held strongholds.
A major success in that operation was the recapture of the rich farmlands around the town of Muqdadiyah, where the jihadists had held sway for more than a year.
However Al-Qaeda still maintains a grip on other parts of the province.
Suicide bombers also struck in Iraq's main northern city of Mosul, another Al-Qaeda stronghold.
Police Major Shahab Ahmed said five people were killed and six wounded when a suicide bomber blew up his vehicle near a police patrol in the Al-Noor neighbourhood in the east of the city.
Four people were killed and five wounded when a second bomber blew himself up close to a police patrol in the Ras al-Jad'a district of the city centre, he added.
Doctor Ahmed Jassim from Mosul hospital confirmed that nine bodies had been brought in from the two attacks.
A car bomb also exploded in Mosul wounding six people, Ahmed said.
In the capital, Electricity Minister Karim Wahid escaped unharmed when a roadside bomb exploded in east Baghdad, wounding three of his bodyguards, security officials said.
Tuesday's bloodshed came as US commanders hailed a fall in overall violence in Iraq to a four-year low.
The declining violence levels have helped clear the way for the US military to withdraw the last of the five additional brigades it deployed last year as part of a troop surge aimed at reining in sectarian violence, particularly in Baghdad and adjacent regions.