The pilgrims were heading to the shrine city to observe a religious ceremony that marks the death of Imam Hassan al-Askari at his tomb in the shrine of Ali al-Hadi in the Sunni dominated city.
The shrine of Ali al-Hadi is one of the four most revered Shiite shrines in Iraq. It contains the tombs of Ali al-Hadi, who died in 868 A.D., and Hisson Hassan al-Askari who died in 874 A.D.
The two are the 10th and 11th of the Shiite's 12 most revered Imams. Shiite pilgrims visited the shrine from all over the world.
Three days ago, a car bomb hit a procession of Shiite pilgrims heading to Samarra on the main road near the town of Dujail, some 60 km north of Baghdad, killing six of them and wounding some 40 others.
On Feb. 22, 2006, Samarra's shrine, also called the Golden Mosque, was attacked with a bomb, with its 100-year-old Golden Dome badly damaged, sparking reprisal killings between Shiite and Sunni communities that claimed lives of hundreds of thousands of Iraqis.