Fifteen others were also wounded in the shootout. It is not known how many were national guardsmen.
The checkpoint at al-Nawar came under fire at 6am (0300 GMT), 15km south of Baquba, Iraqi army sources said.
"Three bodies were completely burnt," said Dr Ahmad Fuad.
Eight bodies were received at the hospital, seven of them soldiers and one other a security guard at a nearby building belonging to Iraqi state television, Fuad and security sources said.
"A Caprice-type vehicle managed to force past the first checkpoint and the suicide bomber slammed his car into an inner gate of the police station, causing a large explosion," Lieutenant-Colonel Hassan Salah said.
In a seperate incident, the son of an official close to the influential Shia figure Grand Ayat Allah Ali al-Sistani was shot dead as he walked out of an internet cafe southeast of Baghdad by an unknown assailant.
Ali al-Khatib, the 30-year-old son of Sayyid Habib al-Khatib, was killed on Sunday in the town of Numaniya.
His father, al-Sistani's aide in Wasit province, survived a similar assassination attempt two months ago.
Meanwhile in Ramadi, three Iraqi civilians were killed and nine others injured after a car bomb targeted a US military patrol, injuring some of its soldiers Aljazeera learned.
It was unclear how the civilians were killed.