Iraqi police say bomb blasts have toppled two minarets of the revered Shi'ite Muslim shrine in Samarra, raising fears of a further escalation of sectarian violence.
There were no reports of casualties in the explosions today at the Askariya Mosque. An attack last year destroyed the mosque's famed golden dome and fueled Iraq's descent into sectarian bloodshed.
Police say four Sunni mosques were attacked after the bombings.
The Iraqi government imposed an indefinite curfew in Baghdad and Samarra after the shrine attack.
Prime Minister Nouri al-Maliki said in a nationally televised address that he had increased security around religious sites, and that Iraqi forces responsible for protecting the shrine have been detained for questioning.
Radical Shi'ite cleric Moqtada al-Sadr called for three days of mourning and his Mahdi militia urged restraint. Lawmakers loyal to the cleric suspended participation in parliament in response to the attack.
Sunni religious and political leaders have also appealed for calm.