"The first car exploded at 8.20am (0420 GMT) at the entrance to the base used by Iraqi soldiers and border guards" on Saturday in Sinjar, 420km north of Baghdad, said police Colonel Qassem Jaber.
"A few minutes later the second bomb exploded in the same place," he said.
The attack happened as soldiers and workers entered the base to start work for the day.
Elsewhere, a former member of Kirkuk's city council was shot dead, Reuters reported Iraqi police as saying on Saturday. It was the latest killing of a local official in a city where tensions between Kurds and Arabs run high.
Naif Sabhan al-Jibouri, an Arab tribal leader and former council member, was shot dead outside his home late on Friday, police Colonel Adil Zain al-Abdein said.
Jibouri was said to have developed good ties with Kurdish officials on the council, which Kirkuk's deputy mayor suggested might have been a reason for the killing.
"The first car exploded
at at the entrance to the base used by Iraqi soldiers and border guards. A few minutes later the second bomb exploded in the
Colonel Qassem Jaber,
Over the past two years, more than a dozen local leaders - including Kurds, Arabs and Turkish-speaking Turkmen - have been killed in Kirkuk, a city that draws wealth from huge nearby oil resources and that is claimed by all three groups.
The city is about 250km north of Baghdad.
In the city of Tikrit, north of Baghdad, two membes of Oil pipeline protection force were killed when a suicide bomber blew up his motorcade near the force's patrol.
In the al-Jihad neighbourhood west of Baghdad, a real-estate broker, Samir Abd al-Razzaq, was shot dead by armed men near a bookshop.
The reasons for the killing remain unknown, however. A police officer and a government employee acompanying Abd al-Razzaq were wounded.
A younger brother of a Japanese security worker taken captive in Iraq has said that a dead body shown in internet footage is his brother.
The group, called Army of Ansar al-Sunna, posted a video showing identification papers and a passport bearing the name of Akihiko Saito, 44, a former paratrooper and veteran of the French Foreign Legion, who has been missing in Iraq since 8 May.
The footage, which was not dated but was seen by Reuters on Saturday, showed the body of a dead man lying on his back with blood covering his face. He appeared to resemble Saito's pictures.
"I saw the footage and confirmed that it was my older brother," Hironobu Saito said in a handwritten statement to media organisations, adding that he had conveyed his view to police and to the Japanese Foreign Ministry.
Six Japanese civilians have been taken hostage since the war in Iraq began.
Meanwhile, a website has reported that Abu Musab al-Zarqawi is in good health and back leading operations in Iraq after being wounded.
The Jordanian fugitive has a
$25 million price on his head
Conflicting statements about the alleged leader of al-Qaida in Iraq have appeared on the internet recently after the group announced on Tuesday that al-Zarqawi had been wounded.
But a statement on Friday said: "Our sheikh is in good health and is running the jihad (holy war) himself and has been overseeing the details of operations up to the time this statement was prepared," a group spokesman said in a posting issued on websites.
Iraq's most wanted
The authenticity or origin of the websites has not been independently verified.
Washington has offered a $25 million bounty for al-Zarqawi.
Also, the US military announced that a rocket-propelled grenade had killed a US marine in western Iraq.
The marine was assigned to the II Marine Expeditionary Force and killed on Thursday in Haditha, 220km northwest of Baghdad, during Operation New Market.