BAGHDAD, Iraq — Two bombs killed 22 people in northern Iraq today as the government tried to tamp down violence and head off civil war a day after Sunni-Arab insurgents killed 215 people in an attack on Baghdad's Sadr City slum that intensified Shiite anger at the United States.

The blasts in Tal Afar, 260 miles northwest of Baghdad, involved explosives hidden in a parked car and in a suicide belt worn by a pedestrian that detonated simultaneously outside a car dealership at 11 a.m., said police Brig. Khalaf al-Jubouri. He said the casualties — 22 dead, 26 wounded — were expected to rise.

In Baghdad, followers of radical Shiite cleric Muqtada al-Sadr threatened to boycott parliament and the Cabinet if Prime Minister Nouri al-Maliki meets with President Bush in Jordan next week, a member of parliament said. Bush and al-Maliki were scheduled to meet Wednesday and Thursday in Amman.

The al-Sadr bloc in parliament and government is the backbone of al-Maliki's political support, and its withdrawal, if only temporarily, would be a severe blow to the prime minister's already shaky hold on power.

Legislator Qusai Abdul-Wahab, an al-Sadr follower, said in a statement that U.S. forces were to blame for Thursday's bombings in Sadr City that killed 215 people and wounded 257 because they failed to provide security. The attack was the deadliest of the war so far.

"We say occupation forces are fully responsible for these acts, and we call for the withdrawal of occupation forces or setting a timetable for their withdrawal," Abdul-Wahab said.

Al-Sadr's followers hold six Cabinet seats and have 30 members in the 275-member parliament.

Al-Sadr also challenged sheik Harith al-Dhari, the Sunnis' most influential leader who heads the Association of Muslim Scholars, to issue a fatwa, or religious edict, that condemned Sunni attacks on Shiites.

The Shiite cleric said al-Dhari should ban Sunnis from joining al-Qaida in Iraq and organize the reconstruction of the Shiite Golden Dome mosque in Samarra, north of Baghdad. Suspected al-Qaida bombers blew the shrine apart on Feb. 22, igniting the sectarian bloodshed.

As funeral processions were held in Sadr City today, several mortar rounds hit the Um al-Qura mosque, headquarters of Association of Muslim Scholars in west Baghdad's Ghazaliyah neighborhood, wounding four of the guards.

In Baghdad's mostly Shiite neighborhood of Hurriyah, clashes between Shiite militiamen and Sunni insurgents armed with machine guns and rocket-propelled grenades broke out near a Sunni mosque, residents said. No casualties were yet reported.

Three mortar rounds also exploded near the Abu Hanifa mosque, Sunni Islam's most important shrine in another area of Baghdad, wounding one guard, said its sheik, Samir al-Obaidi. A mortar round crashed through the dome of the structure Thursday night, within hours of the Sadr City attack.

In the Shiite bastion, hundreds of men, women and children beat their chests, chanted and cried as they walked beside vehicles carrying the caskets of their loved ones.

Baghdad remained under a 24-hour curfew aimed at stopping widespread sectarian violence. But al-Maliki, himself a Shiite, ordered police to guard the processions carrying victims of Thursday's attacks by Sunni Muslim insurgents in Sadr City to Najaf, the holy Shiite city where they will be buried.

In the well-coordinated Sadr City attack, Sunni insurgents blew up five car bombs and fired mortars, forcing Iraqi leaders into a meeting aimed at containing the growing sectarian war.

Shiite mortar teams quickly retaliated, firing 10 shells that badly damaged the Abu Hanifa mosque.