Iraqi Prime Minister Nouri al-Maliki says he has increased security at religious sites, after bomb blasts toppled two minarets of the revered Shi'ite Muslim shrine in Samarra.
Mr. Maliki also said in a televised address that Iraqi forces responsible for protecting the shrine have been detained for questioning.
There were no reports of casualties in the explosions at the Askariya Mosque early Wednesday. Al-Qaida-linked militants are suspected in the bombing.
Iraqi officials imposed a curfew in Baghdad and Samarra after the shrine attack.
Police say four Sunni mosques were attacked after the bombings.
Radical Shi'ite cleric Moqtada al-Sadr called for three days of mourning, and his Mahdi militia urged restraint. Sunni religious and political leaders also appealed for calm.
An attack last year destroyed the famed golden dome of the Askariya Mosque and fueled Iraq's descent into sectarian bloodshed.
Elsewhere in Iraq, a suicide bomber killed five policemen at a police station in the town of Mandali, near the Iranian border. Another suicide bomber killed four policemen at a checkpoint in the northern city of Ramadi.
Also, the editor-in-chief of Iraq's state-owned al-Sabah newspaper, Flayeh Wadi Mijdab was kidnapped in Baghdad.
Meanwhile, the U.S. military said a roadside bomb killed a U.S. soldier in Baghdad Monday. Another U.S. soldier was killed Tuesday when his vehicle hit a bomb in the capital, while a U.S. Marine died in combat operations in al-Anbar province.