Updated

BAGHDAD -- An Al Qaeda front group in Iraq has claimed responsibility for the two deadliest attacks on Shiites since the U.S. military completed its withdrawal last month, underlining an escalating sectarian security and political crisis that threatens to drive the country toward civil war.

A surge in attacks since the U.S. pullout has killed more than 200 people last month and raised fears of a reprise of a conflict five years ago that was close to all-out civil war. And now, there are no American troops to act as a buffer between Sunnis and Shiites.

A statement by Al Qaeda's Islamic State of Iraq on Monday said "Sunni heroes of heroes" infiltrated Shiite processions with explosive vests, killing scores of "nonbelievers and Iranian agents" during Arbaeen commemorations, the most sacred times for Shiite Muslims.

The most bloodiest of the Arbaeen attacks Al Qaeda claimed was the Jan. 5 wave of apparently coordinated bombings in Baghdad and outside the southern city of Nasiriyah that killed 78 people.

The second came nine days later in a blast near the southern city of Basra. At least 53 pilgrims were killed.

Al Qaeda was one of the main U.S. enemies during nine years of war in Iraq. The group was behind some of the deadliest attacks on U.S. soldiers, Iraqi security forces and American-backed government institutions.

Since the last American soldiers left the country Dec. 18, Al Qaeda and other Sunni militants have stepped up attacks against the Shiite majority to undermine confidence in the government of Prime Minister Nouri al-Maliki and the ability of his security forces to protect the people.
Alongside the violence, sectarian-based politician clashes have intensified.

On Monday, Iraqiya parliamentarian Haidar al-Mulla said he was informed that prosecutors were seeking to charge him for insulting the country's judiciary by publicly questioning its independence from al-Maliki's government.

Al-Mulla said he received a notice from the parliament that authorities have requested a vote to strip him of parliamentary immunity in apparent effort to clear the way for his prosecution.

Al-Mulla, who is a Shiite member of the overwhelmingly Sunni Iraqiya bloc, said the efforts are part of a "vicious campaign against Iraqiya" that underlines the authorities' resolve to squelch any criticism of al-Maliki's five-year rule.

"We will not be silenced. I have the right to express my opinion and criticize inappropriate acts," al-Mulla told The Associated Press by telephone. "We will continue our work and expose any mismanagement of affairs in this country," he added.

Al-Maliki's government set off the political crisis in December by issuing an arrest warrant against the country's top Sunni official, Vice President Tareq al-Hashemi, charging him with running death squads. He denied the charges and escaped to the autonomous Kurdish area, out of reach of authorities in Baghdad.

Leaders of al-Hashemi's Sunni-backed Iraqiya allies accused the prime minister of sectarian bias and of trying to push the bloc out of the government to consolidate his own grip on power.

In protest, Iraqiya launched a boycott of the parliament and Cabinet sessions that brought government work to a standstill.

Lawmakers ended the parliament boycott last week, but the bloc's nine ministers stayed away from the weekly Cabinet session. Iraqiya has not confirmed if the ministers will attend the next weekly meeting, set for Tuesday.