A bomb rocked Iraq's parliament building in the heavily fortified Green Zone on Thursday, killing at least eight people, two lawmakers among them, in a stunning security breach in the third month of a US-Iraqi crackdown on violence in the capital, officials said. At least 20 people were wounded in the attack. Mohammed Awad, a member of the Sunni National Dialogue Front, was killed in the blast, said Saleh al-Mutlaq, the leader of the party, which holds 11 seats in Iraq's legislature. Another female Sunni lawmaker from the same list was wounded, he said. A security official at the parliament building said a second lawmaker, a Shi'ite member, was also killed. He spoke on condition of anonymity because he was not authorized to speak to the media. The explosion took place in a cafeteria while several lawmakers were eating lunch, said Muhammad Abu Bakr, who heads the media department at the parliament. "Several people were wounded, including members of parliament and some employees," Bakr said. A spokesman for the US Embassy in Baghdad, which is also in the Green Zone, said no Americans were injured in the blast. "We are aware of reports of an explosion in the Green Zone. We are investigating the nature and source of the explosion," spokesman Lou Fintor said. "No Embassy employees or US citizens were affected." Apparently concerned that an attack might take place, security officials at the parliament were using sniffer dogs earlier Thursday as people entered the building - a rare precaution. Earlier Thursday, at least 10 people were killed after a suicide truck bomb exploded on a major bridge in Baghdad, collapsing the steel structure and sending cars toppling into the Tigris river below, police and witnesses said. Twenty-six others were injured the morning's blast, according to hospital officials, and that toll was expected to rise.