The blast is said to have occurred Wednesday, during military operations aimed at disrupting the flow of explosives into the capital.
Meanwhile, Sunni lawmakers ended their five-week boycott of parliament Thursday, raising hopes the factious assembly can make progress on benchmark legislation demanded by Washington.
The 44 members of the Iraqi Accordance Front attended Thursday's session after striking a deal with other blocs to reinstate the Sunni speaker, Mahmoud al-Mashhadani, who was ousted by the Shiite-dominated assembly last month for erratic behavior.
Al-Mashhadani is expected to gracefully resign after presiding over a number of sessions. Shiite legislator Hassan al-Suneid, an aide to Prime Minister Nouri al-Maliki, said al-Mashhadani's return came after secret conditions that should not be made public.
The Sunnis ended their walkout two days after Shiite lawmakers loyal to anti-U.S. cleric Muqtada al-Sadr ended their boycott after officials accepted their demands for rebuilding a Shiite shrine damaged by bombings.
Those two boycotts had paralyzed the 275-member parliament, which is under strong criticism from U.S. critics for failing to approve key legislation and for plans to take a month's vacation in August at a time when American and Iraqi troops are dying on the battlefield.
U.S. officials also made public Tuesday charges of premeditated murder being brought against two soldiers in connection with the death of an Iraqi last month.
Sgt. 1st Class Trey A. Corrales, of San Antonio and Spc. Christopher P. Shore of Winder, Ga., were charged with one count of murder in the death, which allegedly occurred June 23 near the northern city of Kirkuk, the military said in a statement.
The soldiers charged with the premeditated murder of an Iraqi are assigned to Headquarters and Headquarters Company, 2nd Battalion, 35th Infantry Regiment, which is part of the 25th Infantry Division based in Hawaii. The unit is attached to Multinational Division - North.
The battalion commander, Lt. Col. Michael Browder, was relieved of his command in connection with the investigation although he is not a suspect and has not been charged, the military said.
No further details were released, but the statement noted that the charges are allegations and neither of the two soldiers has been convicted.
The charges were revealed on the same day that a military jury at Camp Pendleton in California of conspiring to murder an Iraqi man in a bungled attempt to abduct and kill a suspected insurgent in Hamdania.
In other recent developments: