The bombing of the Askariya shrine, famous for its golden dome, caused the 30-member bloc loyal to radical cleric Muqtada al-Sadr to suspend its membership in Iraq's parliament and raised fears of renewed sectarian violence.
No casualties were reported from Wednesday's attack. It was unclear how the perpetrators could have gotten past security to topple the mosque's golden minarets that flanked the dome's rubble.
Iraq's government immediately imposed a curfew on vehicle traffic and large gatherings in Baghdad in hopes of warding off further attacks.
But before the curfew took effect, insurgents set fire to a Sunni mosque in western Baghdad, police said. A sole guard escaped, and the mosque was empty at the time, the Associated Press reported.
Police also said a Shiite shrine was blown up north of Baghdad, while two Sunni mosques were bombed south of the capital, according to the AP.
Iraq's top Shiite cleric Grand Ayatollah Ali al-Sistani called on "believers to exercise self-restraint and avoid any vengeful act that would target innocent people or the holy places of others."
Shiite Prime Minister Nouri al-Maliki blamed al-Qaida for the attack, saying that security personnel, who had been guarding the mosque since the Feb. 22, 2006, bombing, would be detained and questioned as part of the investigation.
The top U.S. commander in Iraq, Gen. David Petraeus, and U.S. Ambassador Ryan Crocker also blamed al-Qaida, saying in a joint statement, "This brutal action on one of Iraq's holiest shrines is a deliberate attempt by al-Qaida to sow dissent and inflame sectarian strife among people of Iraq. It is an act of desperation."
The 30-member bloc of al-Sadr supporters said they would boycott the parliament until the government took "realistic" steps to rebuild the Askariya shrine.
