BAGHDAD (AP) _ Saboteur bombers destroyed the two minarets of a revered Shiite shrine in Samarra early Wednesday, in a repeat of the 2006 attack that shattered its famous golden dome and unleashed a wave of retaliatory sectarian violence that still bloodies Iraq. Sunni extremists of al-Qaida were quickly blamed.
The assault on the Askariya Shrine, one of the holiest in Shiite Islam, immediately stirred fears of a new round of intra-Muslim bloodshed, and prompted the 30-member bloc of radical Shiite cleric Muqtada al-Sadr to suspend its membership in Iraq's parliament, threatening a deeper political crisis.
To ward off a surge of violence, Prime Minister Nouri al-Maliki quickly imposed an indefinite curfew on vehicle traffic and large gatherings in Baghdad.
It wasn't clear how the attackers evaded the shrine's guards to mount the stunning operation, detonating the blasts around 9 a.m., and bringing down the two slender golden minarets that flanked the dome's ruins at the century-old mosque. No casualties were reported.
Policemen at the shrine were subsequently detained and will be questioned as part of the investigation, al-Maliki said.
In addition to ordering the curfew, al-Maliki's office said he met with the U.S. commander, Gen. David Petraeus, and U.S. Ambassador Ryan Crocker to ask that U.S. reinforcements be sent to Samarra, 60 miles north of Baghdad, and that U.S. troops in the capital go on heightened alert.
The U.S. command had no immediate comment on military moves. Crocker and Petraeus later released a statement calling the attack and ``act of desperation'' and ``a deliberate attempt by al-Qaida to sow dissent and inflame sectarian strife among the people of Iraq.''
In neighboring Shiite Iran, which has been accused of funding and arming Shiite militias in Iraq, President Mahmoud Ahmadinejad blamed U.S. forces for failing to prevent the mosque attack, and threatened to halt regional cooperation to stop Iraq's spiraling violence.
In a nationally televised address, al-Maliki said he had ordered security forces to bolster protection of Iraq's religious shrines and mosques. The Shiite prime minister also warned against reprisal sectarian attacks.
An official close to the prime minister, citing intelligence reports and speaking on condition of anonymity because of the sensitivity of the information, said the bombing was likely the work of al-Qaida, whose militants have recently moved into Samarra from surrounding areas.
The powerful blasts shook the town, sending a cloud of dust into the air, said Imad Nagi, a storeowner 100 yards from the shrine. ``After the dust settled, I couldn't see the minarets anymore. So, I closed the shop quickly and went home,'' he said.
Police in the area around the shrine began firing into the air to keep people away, witnesses said, and Iraqi army and police reinforcements poured in. The Interior Ministry said a national police force was ordered to move immediately to Samarra.
A U.S. military official in the area, speaking on condition of anonymity because he wasn't authorized to release the information, said Samarra remained calm.
In western Baghdad, just before the curfew was to take hold, Shiite militiamen carrying light weapons fanned out across the religiously mixed Jihad neighborhood, police said. No violence was reported.
The reaction was swift in Shiite-dominated southern Iraq. Black banners were hoisted outside the Najaf residence of radical cleric al-Sadr, who called for three days mourning and peaceful demonstrations to mark the minarets' destruction and criticized the government for not doing enough to protect the site.
He also said the U.S. occupation is ``the only enemy of Iraq'' and ``that's why everyone must demand its departure,'' or a timetable for its departure.
Later, in Baghdad, the 30 members of the Sadrist bloc in parliament issued a statement saying they were boycotting parliament until the government takes ``realistic'' steps to rebuild the Askariya shrine. The move by the Sadrists, whose support for al-Maliki has recently waned, is likely to weaken the Shiite-dominated government and delay adoption of a series of laws needed to build national reconciliation in Iraq.
Last year's surge in execution-style killings, largely blamed on Shiite militias, had begun to decline in Baghdad in February at the start of a major U.S.-Iraqi security push, but violence has recently been rising.
The Askariya shrine's dome was destroyed on Feb. 22, 2006, in a bombing blamed on Sunni Muslim militants believed linked to al-Qaida. The mosque compound and minarets had remained intact but closed afterward.
The mosque contains the tombs of the 10th and 11th imams _ Ali al-Hadi, who died in 868, and his son, Hassan Askariya, who died in 874. Both are descendants of the Prophet Muhammad, and Shiites consider them to be among his successors.
The shrine also is near the place where the 12th imam, Mohammed al-Mahdi, disappeared. Al-Mahdi, known as the ``hidden imam,'' was the son and grandson of the two imams buried in the Askariya shrine. Shiites believe he will return to Earth restore justice to humanity.
After last year's bombing, the mosque was guarded by about 60 Federal Protection Service forces and 25 local Iraqi police who kept watch on the perimeter, according to Samarra city officials.
In the immediate aftermath of that bombing, U.S. officials and others had promised to help rebuild the landmark dome, completed in 1905, but no rebuilding has begun.
Iraq has been plagued by violence since the war started in 2003, but the carefully orchestrated 2006 explosion touched a nerve. The bombing unleashed Shiite militias, who ignored appeals for calm and instead attacked Sunni clerics and mosques. Nearly 140 people were killed the next day.
In other violence, a suicide bomber blew himself up at a police station in a town near the Iranian border, killing five Iraqi policemen and wounding 10, the mayor said. In the western city of Ramadi, a suicide bomber killed four policemen at a checkpoint, police said.
In northern Iraq, militants blew up part of a bridge in the country's fourth attack on a span in as many days, police said.
The attackers had planted explosives under the Zikaytoon overpass near Kirkuk, about 180 miles north of Baghdad, said police Brig. Sarhat Qader. No one was wounded, he said.