Lt. Col. Mahmoud Abdul Aziz of the Iraqi Interior Ministry announced the death toll, which is expected to rise.
In the Iraqi parliament, meanwhile, parties were in talks to form a coalition aimed at limiting the power of radical Shiite cleric Muqtada al-Sadr and Sunni extremists within the government.
The attack took place in Tarayan Square, a market across the Tigris River from the international Green Zone, where day laborers, mostly Shiites, gather for work. Some witnesses described two simultaneous explosions, the truck and a car parked nearby.
Witness Maitham Ali described bodies flying through the air after the blast and one wounded survivor searching for his brother and then carrying him out of the wreckage before both were taken to the hospital, the New York Times reported.
Prime Minister Nuri al-Maliki, a Shiite, denounced the attack, blaming it on Sunni religious extremists "and their Saddamist allies."
The speaker of the Iraqi Parliament, Mahmud Mashhadani, a Sunni, said the attack was the work of "outlaws and those without a religion" who targeted poor people who were trying to feed their families, ''turning them into pieces of flesh.'' He called on all armed groups to observe a two-month truce.
Also in Baghdad Tuesday, major political parties were trying to form a coalition to limit al-Sadr's influence within the government, senior Iraqi officials told the New York Times.
Sadr controls a militia estimated to be about 60,000 strong that has clashed with American forces and is accused of reprisal killings against Sunni Arabs.
The two main Kurdish groups, the most influential Sunni Arab party, and the Iranian-backed Shiite party, invited Prime Minister al-Maliki to join them, but so far he has been reluctant to do so.
President Bush is said to be supporting the move, following a meeting with Abdul Aziz al-Hakim, the leader of the Iranian-backed Shiite party, last week and a planned event with Tariq al-Hashemi, leader of the Sunni Arab party, this week.
In a memo leaked last month to the Times, the president's national security adviser, Stephen Hadley, wrote that the United States should press Sunni Arab and Shiite leaders to support al-Maliki and help him build "an alternative political base."