Iraqi police say clashes between security forces and armed members of a Shi'ite sect have killed at least 40 people in the southern cities of Basra and Nasiriyah.
Officials said the fighting began Friday when members of the "Soldiers of Heaven" sect's militia launched an attack on police and civilians.
The attacks occurred despite curfews imposed in 10 southern provinces, Baghdad and northern Diyala province during the 10-day annual Ashura religious observances -- one of the holiest events for Shi'ite Muslims.
The high point of Ashura takes place Saturday in Karbala. Some 2.5 million people from across Iraq and the rest of the Muslim world are expected to participate in a commemoration of the seventh-century death in battle of Imam Hussein, a grandson of Islam's Prophet Mohammed.
Ashura observances in southern Iraq in previous years have been marked by sectarian clashes.
In other news, U.S. Secretary of Defense Robert Gates says the frequency of roadside bomb attacks in Iraq or I.E.D. attacks - the U.S. military's term for "improvised explosive devices", is increasing.
Speaking Friday in South Carolina, at a military facility that prepares armored vehicles for use in Iraq, Gates said there were as many I.E.D. attacks in the first half of January as there were for the entire month of December.
Separately, the U.S. military said Friday that coalition forces killed 13 terrorists and detained three suspects during operations targeting al-Qaida networks in central and northern Iraq.
Some information for this report provided by AP, Reuters and AFP.