The government blamed al-Qaida in Iraq Saturday for the killing of a prominent Sunni lawmaker, as political figures joined together across sectarian lines in a show of solidarity against a return to violence. Sunni and Shi'ite lawmakers called the slaying of Harith al-Obeidi - the leader of the largest Sunni bloc in parliament - an attack against moderation, as they took turns at the podium to call for a united front against terrorism. Al-Obeidi and a bodyguard were gunned down as they left a mosque after Friday prayers. The Iraqi parliament held a special session to honor him after a funeral service at Baghdad's Convention Center in the guarded Green Zone. US and Iraqi officials have warned violence is expected to increase as insurgents try to rekindle sectarian violence before national elections scheduled for early next year. The brazen daylight shooting in a heavily guarded area also raised new concerns about the ability of Iraqi forces to maintain security with US forces withdrawing from cities by the end of the month. The attack took place in a western Baghdad neighborhood that was a Sunni insurgent stronghold until local tribal leaders turned against al-Qaida in Iraq. Shi'ite lawmaker Jalaluddin al-Saghir called on Iraqis to unite against a resurgence of violence, which has fallen sharply over the past two years. "They think they can mess with the political process and those supporting it when the American forces leave," he said at the parliamentary session. "We have to improve the security forces ... to make it impossible for such killers and criminals to bring us back to square one of civil and sectarian wars," he said. The 47-year-old lawmaker had been a champion of prisoners' rights and was at the center of a stormy parliamentary debate over claims of torture in Iraqi jails. He was known for his advocacy for both Sunni and Shi'ite detainees. Colleagues said that the day before his death, he had called on parliament to summon officials from the interior and defense ministries, which oversee the jails, to respond to the allegations. That raised suspicion that his slaying may have been linked to his campaign on behalf of detainees. But Maj. Gen. Abdul-Karim Khalaf, the Interior Ministry spokesman, said the evidence so far indicates al-Qaida in Iraq was behind the attack. He declined to elaborate while the investigation is ongoing. The Sunni terror network and other insurgents have frequently targeted other Sunnis who are perceived as cooperating with the US-backed government's efforts to promote national reconciliation. During the funeral, which was broadcast on all of Iraq's television stations, Prime Minister Nouri al-Maliki, a Shi'ite, and lawmakers from all sects vowed the killing would not set back security gains in Iraq. Two caskets holding al-Obeidi and his bodyguard were carried by an Iraqi military honor guard. Hundreds of people later gathered for his burial in the main Sunni cemetery near the Abu Hanifa mosque in northern Baghdad. "His assassination is an attempt to embarrass al-Maliki's government, the reconciliation project and renew the chaos and turmoil of the past," said Sheik Kheir-Allah al-Basri, a Shi'ite lawmaker. Sunni lawmaker Dhafir al-Ani applauded al-Obeidi's political moderation. "Al-Obeidi established a school of moderation inside the parliament. He expressed his position with courage and without any fear," he said. Al-Obeidi took the helm of the Iraqi Accordance Front - which holds 44 seats in the 275-member parliament - in May after his predecessor, Ayad al-Samarraie, became the parliamentary speaker. He was the fourth Iraqi member of parliament to be killed since the US-led invasion in March 2003. In other violence, the US military announced that an American soldier was killed by a roadside bomb Friday in Baghdad. At least 4,312 members of the US military have died in Iraq since the war started, according to an Associated Press count.