Police and provincial officials say the assailants drove up to the checkpoint near the al-Qaim border town and opened fire. They say the gunmen shot an eighth soldier several times but left him alive "to convey a message to the Iraqi army."
Friday's attack comes on a bloody day in Iraq in which at least 27 people were killed,and several people killed in a pair of car bombings north of Baghdad.
Provincial council member Sheik Efan Saadoun blamed the army checkpoint attack on a decision to replace police with Iraqi soldiers who are less familiar with the local surroundings.
Car bombs, meanwhile, tore through two neighborhoods in restive cities north of Baghdad in separate attacks targeting a police captain and a provincial council member.
One blew up in the northern city of Tuz Khormato about 50 yards (meters) from the house of Niazi Mohammed, a Turkomen member of the Salahuddin provincial council, according to police.
City police chief Col. Hussein Ali said at least eight people were killed and 69 wounded in the blast, which left some 20 houses heavily damaged. A second car bomb was discovered about 100 yards (meters) from the blast site, but it did not explode, Ali said.
"We believe that al Qaeda was behind today's attack in order to destabilize security and re-ignite sectarian strife," he said.
Mohammed, who was not home at the time of the blast, condemned the attack, saying it only hurt innocent civilians.
"My job in the provincial council is to serve people and it has nothing to do with security forces," he said.
Another blast targeted the house of police Capt. Mustafa Mohammed in Baqouba northeast of Baghdad, killing two neighbors and wounding 27 other people, including some of the officer's relatives, police said.
The officials reported the violence on condition of anonymity because they weren't authorized to release the information to the media.
Hours later, a bomb exploded at the gate of a house, killing three residents, a man and two women, who sold tea and water to soldiers at a nearby Iraqi army checkpoint, according to police and hospital officials.
Police said the residents had ignored insurgent warnings to cut off relations with the soldiers.