The claim for the Tuesday blast, posted on militant Web sites, was the second this week from the Islamic State of Iraq. The group previously said it carried out suicide car bombings at three Baghdad hotels on Monday that claimed at least 41 lives.
The Islamic State of Iraq, which includes al-Qaida in Iraq and other allied Sunni insurgent factions, has now claimed responsibility for all major bombings in Baghdad since August attacks at the Foreign and Finance ministries.
The latest claim could not be independently verified, but the group has used such Web sites in the past to take responsibility for attacks.
The statement described the bombing on the Interior Ministry's forensic lab as the "second phase" of its campaign this week. It also vowed more strikes against offices and institutions of the Shiite-led government.
The attacks appear aimed at rattling and embarrassing the U.S.-backed leadership in Baghdad before national elections on March 7. Prime Minister Nouri al-Maliki has made the overall drop in violence around Iraq the centerpiece of his campaign.
But his government has faced an outcry from parliament members and political critics for security lapses that have allowed a string of high-profile attacks in the heart of Baghdad over the past six months.
