The attack by the bomber, who detonated an explosives-rigged vehicle at the headquarters of the Hafr Zawiyah border post in Iraq’s vast Anbar province, also wounded 14 guards.
An army lieutenant colonel said the bomber was dressed in a military uniform with captain’s insignia and was driving an explosives-rigged military vehicle.
Hussein al-Goli, a lieutenant colonel in the border guards, was among the dead, the army officer said.
Imad Ahmed, a local official responsible for the Rutba area in Anbar, confirmed the toll.
There was no immediate claim of responsibility for the attack, but suicide bombings are a tactic almost exclusively employed by the Islamic State jihadist group in Iraq.
IS has overrun significant territory in Anbar province, which stretches from the borders with Syria, Jordan and Saudi Arabia to the western approach to Baghdad, including provincial capital Ramadi.
Iraqi security forces are battling to retake Ramadi, and seized a large area on the southwest side of the city last week.