Earlier, a British soldier was killed in a roadside bomb blast in southern Iraq, while a US Marine died in a bomb attack north-west of Baghdad.
The latest bomb attacks came as the military announced the end of a massive four-day offensive in western Iraq.
Operation Lightning was launched as a direct challenge to the bloody wave of militant attacks that have killed more than 700 people since the April 28 announcement of Iraq’s new Shi’ite-led government.
But despite the heavier-than-normal Iraqi police and army presence in the capital and on its southern and northern outskirts, insurgents kept up their steady pace of violence.
A suicide attacker detonated a car bomb outside the heavily fortified Iraqi Oil Ministry earlier yesterday killing two security guards, said ministry spokesman Assem Jihad.
The blast happened when the militant tried to ram a Volkswagen sedan packed with explosives through the gate of the ministry building, located in eastern Baghdad, said Mr Jihad.
Guards fired on the vehicle which exploded about 20 metres from the gate.
Before dawn, insurgents attacked an Iraqi army checkpoint in Youssifiyah, 12 miles south of Baghdad, killing nine soldiers and injuring one, said Dr Dawood Al Taaei of nearby Mahmoudiya hospital.
Gunmen also killed two police sergeants employed by the Iraqi Cabinet in a drive-by shooting in Dora.
Another two police commandos were killed and five injured in a car bomb blast at Madain about 14 miles south-east of Baghdad.
A suicide car bomber, apparently targeting a US convoy, exploded his vehicle and killed two Iraqis and injured nine others in northern Iraq.
“With the escalating operations by security forces, we expect such reactions coming to the surface, but this will have no affect on the operations,” Laith Kuba, spokesman for Iraqi Prime Minister Ibrahim al-Jaafari, said.
The first of more than 40,000 soldiers and police were deployed to Baghdad’s streets early yesterday, erecting checkpoints on the southern and northern outskirts of the city in the largest Iraqi-led offensive launched since Saddam Hussein was ousted.
Iraqi security forces searched hundreds of vehicles and raided several houses, described as “terrorist dens” in Dora, arresting several suspects.
“We set up these checkpoints in order to arrest all those insurgents trying to destroy this country and we will hit them with an iron fist,” said Iraqi army sergeant Ali al-Khazali while manning a checkpoint in Dora.
Baghdad will be divided into two sectors, Karkh on the west bank of the Tigris river that separates the city, and Risafa on the east.
Separately, the US military announced the end of Operation New Market, a four-day offensive centred on the western Iraqi town of Haditha aimed at disrupting insurgent activities.