The attacker drove an explosive-rigged Humvee into a military headquarters in the town of Garma, where government forces and allied militias have been battling Islamic State militants, a police officer said.
The dead included three soldiers and three militia members, he added. Nine other troops were wounded. A medical official confirmed the casualty figures. Both officials spoke on condition of anonymity as they were not authorized to release information.
Recapturing Garma is an essential step to tighten the grip around the city of Fallujah, about 65 kilometers west of the capital, which has been under IS control since early last year.
Meanwhile, Iraq's Prime Minister Haider al-Abadi received his Canadian counterpart, Stephen Harper, in Baghdad. Canada is part of the US-led international coalition that supports the Iraqi military with airstrikes, training and weapons.
Al-Abadi hailed Canada's role in that coalition as "essential" and called on the international community to join forces against the extremist threat as "terrorism is not only threatening Iraq, but the region and the whole world."
Al-Abadi lauded his country's security forces and vowed to retake all IS-held areas. The militant group controls large areas of Anbar province and Iraq's second largest city, Mosul.
"Daesh is now retreating, Daesh is now weak," he said, using the Arabic acronym for the Islamic State group. "We liberated all areas in Diyala (province), the majority of Salahuddin (province), Baghdad is more secure than any time before, we are now liberating Anbar and after it, we will go to Mosul.
