About two million pilgrims have marched through the Iraqi city of Karbala to mark Ashura - one of the holiest events in the Shia religious calendar.
Ceremonies were held across Iraq
Security was stepped up in the holy city, with over 20,000 Iraqi troops and police deployed to prevent violence.
Tensions were high after dozens died in fierce fighting on Friday between police and a Shia cult in the two southern cities of Basra and Nasiriya.
Clashes between Iraqi troops and the cult last Ashura left 263 people dead.
The violence sparked fears of further attacks during Saturday's climax of the Ashura ceremony, which commemorates the martyrdom at Karbala of Imam Hussein, grandson of the Prophet Muhammad, in 680 AD.
Ashura ceremonies have also been targeted in the past by Sunni insurgents.
But while violence was reported elsewhere in the country, Karbala remained calm.
Thousands marched through the streets of Karbala and other cities in blood-soaked processions, striking their heads with swords, beating their chests or flagellating themselves to express their grief and devotion.
At least seven people were killed in the northern town of Tal Afar when a rocket hit a crowd gathering to commemorate Ashura, police said.
Earlier, at least two people were killed and several injured in a bomb attack on an Ashura procession in Kirkuk.
Renewed clashes were also reported in Nasiriya between police and gunmen belonging to a Shia cult, the Soldiers of Heaven.
Violence broke out in the southern city and in Basra on Friday after apparently co-ordinated assaults were launched by members of the cult on police and Shia worshippers.
SOLDIERS OF HEAVEN
January 2007: Iraqi officials say 263 cult members killed in fighting in Najaf
Former cult leader Dia Abdul-Zahra Kazim Krimawi, aka Samer Abu Kamar, killed in Najaf battles
Iraqi government claimed cult planned to kill top Shia clerics and declare the Mehdi had come during Ashura
Current leader, Ahmed Hassani Yamani, reportedly claims to be an ambassador of the Mehdi
Several hours after Friday's gun battles began, Prime Minister Nouri Maliki said security forces had re-taken control of the two southern cities.
The fighting in Nasiriya - 375km (235 miles) south-east of Baghdad - began at around midday local time when mortars were fired at a police position in the city, police said.
The bombardment was followed shortly afterwards with an assault by cult members armed with machine guns and rocket propelled grenades, according to officials.
At least 15 people were killed in the ensuing clashes, including a city police commander and seven other officers, police said. A woman civilian and three militants also died.
In Basra, officials said dozens of people were killed after members of the cult went on the rampage attacking police and civilians.
The city's police chief said the leader of the cult in Basra - identified as Abu Mustafa Ansari - had been killed in the fighting along with two other gunmen and two police officers.
Shia factions have been engaged in a power struggle across southern Iraq.
On Friday, the radical Shia cleric, Moqtada Sadr, issued a fresh challenge to the Shia-led government saying he might not extend a six-month ceasefire by his militia, the Mehdi Army.
The truce, due to expire next month, has been credited by the Americans with helping bring about a big improvement in security in Iraq.
But a spokesman for the cleric, Salah Obeidi, said the results had been disappointing because criminal gangs were still operating inside the security forces with government support.
Last year, 263 members of the Soldiers of Heaven were killed in clashes with US-backed Iraqi security forces after officials reportedly uncovered a plot to attack the holy city of Najaf and kill its religious leaders during Ashura.
The Soldiers of Heaven followers are said to believe that the former leader, Dia Abdul-Zahra, who was killed in the fighting, was the Mehdi - a 9th Century messiah.
The cult has since been led by Ahmed Hassani Yamani, who reportedly claims to be an ambassador, rather than a descendent, of the Mehdi.
BBC religious affairs correspondent Frances Harrison says it is believed that the Mehdi did not die but went into hiding and will one day return, accompanied by Jesus, to save the world once it has descended into chaos.