BAGHDAD, Iraq (CNN) -- A suicide attack in Iraq's parliament building on Thursday killed eight people, including two Iraqi lawmakers, and wounded 20, U.S. and Iraqi officials said.
After the attack in the building's cafeteria, more explosives were found near the parliament room and were destroyed in a controlled detonation, according to Iraqi lawmaker Iman al-Asadi.
It is unclear how the bomber was able to pass through the multiple security checkpoints required to enter the parliament building, which is in Baghdad's heavily fortified Green Zone. (Watch how attack illustrates difficulty of Baghdad security Video)
The Associated Press, citing Mohammed Abu Bakr, the parliament's media relations chief, said some security procedures had changed earlier Thursday at a Green Zone entrance near the parliament building.
The entrance's security scanner was not working, Abu Bakr told the AP, and pedestrians entering the zone were subject to hand searches and passed through metal detectors, he said.
U.S. military spokesman Maj. Gen. William Caldwell said that based on "the trends" of the attack, al Qaeda in Iraq is believed to be responsible for the bombing, although he stressed an investigation is under way.
The dead include at least two lawmakers, a Sunni and a Shiite, according to Muhanned Jabbar, an official with the office of Iraq's parliament speaker.
The Shiite lawmaker's identity has not been released. Jabbar identified the Sunni as Mohammed Hassan Awadh, a member of the National Dialogue bloc.
The alliance, which holds 11 parliament seats, is headed by Salih al-Mutlag, a secular Sunni lawmaker who opposes the more powerful Iraqi Accord Front, a Sunni bloc with 44 legislative seats.
At least three lawmakers are among the wounded, according to Jabbar.
The parliamentary speaker, Mahmoud al-Mashhadani, has called for an emergency session Friday morning to show that the attack won't deter lawmakers, Jabbar said.
The explosion happened around 2:30 p.m. (6:30 a.m. ET) as parliament members headed to the cafeteria following Thursday's session, al-Asadi said. The lawmaker said she did not go to the cafeteria but headed to the legal department, where she heard a loud explosion from inside the restaurant.
Lawmakers and everyone inside the building -- which once was Baghdad's convention center -- were immediately put in lockdown as a precaution following the explosion.
In addition to parliament, the center also houses Iraqi government offices.
The Green Zone, a four-square-mile area also known as the International Zone, is the seat of the U.S. military and U.S. diplomatic agencies as well.
There were no American casualties in the blast, according to U.S. officials.
President Bush condemned the attack, saying, "It reminds us ... that there's an enemy willing to bomb innocent people in a symbol of democracy.
"This simply is a place where people have come to represent the 12 million people who voted," Bush said, referring to Iraqi elections. (Watch Bush's statement on cafeteria attack Video)
British Foreign Secretary Margaret Beckett said, "Nothing could highlight more the twisted minds of those who are seeking to disrupt the democratic process in Iraq. Those who carry out these outrageous attacks offer nothing to the Iraqi people except more murder and destruction."
Iraqi Prime Minister Nuri al-Maliki vowed to bring those responsible to justice and said the "despicable crime will not weaken the will of people's representatives, or discourage their determination to continue their role in service of the goals and aspirations of Iraqis."
Lawmaker Sheik Dia'aldin al-Faidh of the United Iraqi Alliance blamed Thursday's attack on terrorist infiltration at the highest levels.
He said there have been security problems in the past, noting that two unexploded suicide vests found inside the Green Zone on March 31 were discovered in the apartments of lawmakers' bodyguards.
Security inside the Green Zone has been compromised in recent weeks, prompting the U.S. Defense Department to recently require all personnel to wear body armor and helmets when outside buildings in the zone, a source there said.
On March 22, two mortar rounds struck inside the Green Zone during a live news conference, causing visiting U.N. Secretary-General Ban Ki-moon to duck in surprise.
On March 27, a U.S. soldier and American contractor were killed and five people were wounded when a rocket landed in the Green Zone.
Truck bomb brings down bridge
A suicide truck bomb exploded Thursday morning on a major bridge in northern Baghdad, sending cars into the Tigris River and killing at least 10 people and wounding 26 others, according to an Iraqi Interior Ministry official..
Video footage showed two large sections in the middle of al-Sarafiya bridge collapsed into the river.
Al-Sarafiya bridge connected the predominantly Sunni Adhamiya neighborhood and Bab al-Muadham, a mixed district.
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