The lunchtime explosion took place in Khalis, 20km northwest of Baquba, Iraqi army Colonel Saleh al-Obeidi said. Baquba is 60km northeast of Baghdad.
Al-Obeidi said the man was wearing an army uniform and waited until soldiers had gathered for lunch before blowing himself up.
The soldiers belonged to the al-Salam battalion of the 2nd brigade of the Iraqi army in Diyala province.
The injured were being evacuated to a nearby hospital, Iraqi army Major Abbas Timimi said.
Earlier on Wednesday, police killed two men in a gunfight in the oil-rich northern city of Kirkuk, a day after a bomber killed 19 people and wounded nearly 81 in the city.
The two men fired on the police patrol from a speeding car in central Kirkuk, police Colonel Burhan Taha said.
A third man was captured, and two police officers were wounded during the gunfight.
Kirkuk has become an area for sectarian tension, and Tuesday's violence was the worst to hit the ethnically mixed city, 290km north of Baghdad, since the war started in March 2003.
On Tuesday, US marines and Iraqi soldiers killed five Iraqi civilians at an entrance to the volatile western town of Ramadi, 115km west of Baghdad, shortly after an attack on a military checkpoint left one Iraqi soldier dead, the military said.
Bulgarian soldiers killed
Separately, two Bulgarian soldiers were killed and another injured late on Tuesday when their vehicle slid from a dyke into a canal about 55km southeast of Diwaniya, a city in south-central Iraq where about 400 Bulgarian soldiers are serving.
Twelve Bulgarian soldiers have died in Iraq. Another three Bulgarians were among 11 civilians killed when a Bulgarian-owned commercial helicopter was shot down on 21 April north of Baghdad.
Meanwhile, in eastern Baghdad, Aljazeera reported that British soldiers were wounded in clashes. More details were not available.
Prime Minister Ibrahim al-Jaafari, speaking in parliament after the Kirkuk attack, accused the fighters of targeting civilians - as the number of people killed by fighters since the 28 April inception of his Shia-dominated government hit at least 1018 people, including US forces.
"They are trying now to avoid the military areas, the areas controlled by the multinational or Iraqi forces and they are now conducting their operations in the markets," al-Jaafari told parliament shortly before a vote of confidence.
Al-Jaafari accused fighters in
Iraq of targeting civilians
Fighters have routinely launched deadly attacks in Kirkuk.
Kurds have long coveted Kirkuk as the capital of an autonomous Kurdish region encompassing all three of their northern provinces.
Ousted president Saddam Hussein forced nearly 100,000 Kurds out of the city as part of an "Arabisation" plan.
Mohamed al-Askari, an expert on Iraq's security and military affairs, told Aljazeera that anti-US fighters are adopting new strategies to counter the government's security plans.
"The attacks take place because the assailants have penetrated into the ranks of the security forces and have some people cooperating with them," he said.
"he number of daily attacks in Baghdad has ranged between 60 to 70 operations but now the attacks have been remarkably reduced in Baghdad, although they have surged in other towns"
Iraqi security expert
"The assailants are well trained and experienced and have their own plans, strategies and manoeuvres."
He added: "Certainly, the government security plan has been a success. The number of daily attacks in Baghdad has ranged from between 60 to 70 operations, but now the attacks have been remarkably reduced in Baghdad, although they have surged in other towns outside Baghdad."