Baghdad, Iraq - Violence left nearly 50 people dead in two major southern cities Friday when members of a shadowy, messianic cult attacked police and fellow Shiite worshippers -- a year after a similar plot was foiled during Shiite Islam's most important holiday.
Iraqi authorities said at least 36 people were reported killed in Basra, Iraq's second largest city, and at least 10 in Nasiriyah, where witnesses said U.S.-led coalition jet fighters and helicopter gunships targeted a police station seized by cult gunmen.
U.S. military spokesman Maj. Brad Leighton said an Iraqi request for air support in the area was approved, but he could not confirm whether airstrikes were carried out. Some clashes raged into the night, raising the possibility of more casualties.
The assaults were launched as hundreds of thousands of Shiites observed the Ashoura holiday by marching, singing and beating their chests to honor the martyrdom of their most beloved saint. Followers of the cult -- the Soldiers of Heaven -- seek to speed the return of another Shiite figure known as a ''Hidden Imam,'' who believers say will bring justice to the world.
A series of recent high-profile attacks is eroding the security gains of the previous six months, when violence dropped across much of the country. The main insurgent group, al-Qaida in Iraq, has carried out many of the attacks against fellow Sunnis who have turned against it. But insurgents also struck with deadly suicide blasts this week against Shiites observing Ashoura.
Friday's clashes pointed to a third problem that shows no signs of easing: Shiites attacking fellow Shiites. The attacks were a reminder of persistent divisions within the Shiite community at a time when the Pentagon is claiming some success in calming armed opposition among the Sunnis.
Shiite factions have been engaged in a power struggle across southern Iraq. On Friday, two prominent Shiite leaders issued fresh challenges to the Shiite-led government in Baghdad.
Radical cleric Muqtada al-Sadr warned he may not extend a six-month cease-fire by his Mahdi Army militia, because security agencies are packed with ''criminal gangs,'' his spokesman said in reference to Shiites from rival groups. The group's cease-fire, due to expire next month, has been a major factor in the reduction in violence.
And Abdul-Aziz al-Hakim, the head of parliament's largest Shiite political bloc, accused Prime Minister Nouri al-Maliki's government and legislators of allowing ''personal whims'' to delay national unity. He urged them to pass stalled legislation on provincial elections and the distribution of Iraq's oil wealth, seen as vital to bringing Sunnis into the political process and stemming support for the insurgency.
On a visit to Baghdad on Tuesday, Secretary of State Condoleezza Rice warned that the recent reduction of violence could prove fleeting if the country's main groups do not reach an enduring agreement on the future of the country.
Al-Qaida in Iraq was expected to be the main threat against this year's Ashoura processions, which Sunni Arab militants have repeatedly targeted with car bombings and mortar attacks that have killed hundreds since 2003.
But it was Shiites who struck.
There were conflicting accounts about how the attacks developed, but all signs pointed to the Soldiers of Heaven cult. Last year, it mounted a ferocious attack after Iraqi security forces raided its stronghold near Najaf to foil an alleged plot to slaughter pilgrims and leading clerics during Ashoura.
Iraqi forces prevailed in last year's battle -- but only after U.S. and British jets blasted the militants with rockets, machine gunfire and 500-pound bombs. Both U.S. and Iraqi reinforcements had to be sent to the fight.
The group's bloody aims are seen as a bid to bring the return of the ''Hidden Imam'' -- also known as the Mahdi -- a descendant of the Prophet Muhammad who disappeared as a child in the 9th century. Shiites believe he will return one day to bring justice to Earth.
Friday's attack began when militants carrying yellow flags or wearing yellow headbands, the cult's color, fired mortars at a police station in Nasiriyah, about 200 miles south of Baghdad. A shootout with police followed.
A police officer said at least 10 people were killed -- seven policemen, including two senior officers, two female civilians and one gunman. He also said more than 50 people were injured after gunmen stormed the building of a quick reaction force in the city. The officer spoke on condition of anonymity because they were no authorized to release information.
Street battles also broke out in Basra, 340 miles southeast of Baghdad, after cultists opened fire on a police patrol. Police torched a mosque belonging to the cult after militants fired at officers from inside, authorities said.
The militant cult members also shot at Shiite worshippers taking part in Ashoura observances, according to Basra Gov. Mohammed al-Waili. No injuries were reported.
''These terrorist groups have opened fire randomly on citizens and Shiite mourners and we are about to eliminate or arrest them,'' the governor said.
Basra police chief Maj. Gen. Abdul-Jalil Khalaf said 30 militants and six security forces were killed. He also said 30 militants were detained.
Khalaf said the leader of the group in Basra, whom he identified as Abu Mustafa al-Ansari, was among those who died.
About eight hours after the clashes began, the government said Iraqi security forces had restored calm in the cities after ''heretics'' attacked Ashoura processions. But gunfire could still be heard in Nasiriyah, and police said they received orders to evacuate an area occupied by gunmen so U.S. forces could take over.
Coalition forces have turned over control to the Iraqis in the provinces of Basra and Dhi Qar, whose capital is Nasiriyah. The ability of the Iraqis to maintain their own security is key to the U.S. strategy for eventual withdrawal from the country.
Iraqi authorities maintained tight security along roads into the Shiite holy city of Karbala, the center of the Ashoura observances, which have been going on for about a week in much of the country. Karbala, about 50 miles south of Baghdad, is home to the tomb of Imam Hussein, the Prophet Muhammad's grandson who was killed during a seventh century battle in the area.
Pilgrims lined up to be searched at the entrance of the twin shrines of Hussein and his brother Abbas, about 350 yards apart. The streets were lined with tents providing tea, milk, food and first aid. The climax of Ashoura -- a massive procession toward the golden-domed Imam Hussein shrine -- comes Saturday morning.
North of Baghdad, a U.S. soldier was killed when a roadside bomb exploded near his vehicle during combat operations, the U.S. military announced. The soldier was not identified.