U.S. military spokesman Major General William Caldwell reported the latest death toll, and said witness accounts indicate that an attacker with a suicide bomb vest was responsible. The explosion occurred in a cafeteria used by lawmakers and journalists.
The dead lawmakers have been identified as Muhammad Awad, a member of the Sunni-led Front for National Dialogue, and Taha al-Liheibi of the Sunni-led Accordance Front.
Several other people were wounded.
U.S. President George W. Bush condemned the bombing as an attack on democracy.
The Iraqi parliament "is a place where people have come to represent the 12 million people who voted," Bush told journalists in Washington. "There's a type of person [who] will walk in that building and kill innocent life, and that is the same type of person [who] is willing to come and kill innocent Americans."
"My message to the Iraqi government is: We stand with you as you take the steps necessary to not only reconcile politically, but also put a security force in place that is able to deal with these kind of people," he added.
U.S. Secretary of State Condoleezza Rice condemned the attack as the work of "terrorists and those who wish to stop the Iraqi people from having a future that would be based on democracy and stability."
Prime Minister Nuri al-Maliki called it a "criminal and cowardly act."
Many Journalists, Lawmakers Present
Layla Ahmad, a correspondent for RFE/RL's Radio Free Iraq, had just left parliament when she heard the blast.
"To get to the [parliament], you need to go through several checkpoints, about five checkpoints, starting with one under the supervision of the Iraqi Army," a Radio Free Iraq correspondent said.
"While we were on the way out of the [parliament building], around 14:30 or a little bit before, a huge blast shook the place where we were," she said. "Then we learned that a blast had taken place inside the building, but we were restricted from going back in, and tight security measures were imposed. People, employees and journalists, were forbidden from leaving the [parliament]."
Ahmad says journalists usually use the busy cafeteria to meet with parliamentarians and today was no exception.
"The cafeteria today was attended by a large number of parliament members, before they convened and after," Ahmad said. "Also, journalists were there -- radio journalists, print journalists, and journalists from satellite TV, who were coordinating interviews with [parliamentary] deputies."
Apparently concerned that an attack might take place, security officials at the parliament were using sniffer dogs earlier today as people entered the building. Ahmad also says security today was tighter than normal.
"To get to the [parliament], you need to go through several checkpoints, about five checkpoints, starting with one under the supervision of the Iraqi Army, where two or three Iraqi soldiers check identification cards and search bags," Ahmad said. "Especially today, two or three U.S. soldiers were with the Iraqi soldiers, and they were checking identification cards."
The Green Zone is home to the Iraqi cabinet, presidency, parliament, the Defense Ministry, and the Iraqi High Criminal Court. It is also home to the U.S. and British embassies.
It is considered by far to be the most heavily guarded object in the capital.
In other developments before today's Green Zone blast, a truck bomb killed at least seven people on a key bridge in northern Baghdad, destroying most of the structure. Two main sections of the Al-Sarafiyah Bridge, a main artery linking east and west Baghdad, collapsed into the river.
Adopting New Tactics
U.S. Army General Ray Odierno discusses new insurgent tactics in Iraq and what the coalition is doing in response. more
Inside The Green Zone
Ordinary Iraqis are unable to enter the Green Zone except on official business. But what they see from outside bears little resemblance to the rest of the capital. more
THE COMPLETE STORY:
RFE/RL's complete coverage of events in Iraq and that country's ongoing transition.