BAGHDAD, Iraq (CNN) -- Bombings killed at least eight people and left dozens injured Thursday in Mosul and Karbala as sectarian violence continued in Iraqi cities.
A car bombing in the northern Iraqi city of Mosul on Thursday killed three police officers, a day after a string of attacks there killed a half dozen people.
Police in Mosul said the bomb exploded at the side of a road in the southern part of the city as a police convoy was driving past. Along with the fatalities, two police officers and a civilian were wounded.
Mosul is the capital of Nineveh province, which still endures the presence of al Qaeda in Iraq, the Sunni militant group.
Iraqi Interior Ministry officials said a bomb was the probable cause of an explosion Thursday near a shrine in Karbala, which killed at least five Shiite pilgrims and wounded 50. Three days earlier, bombings targeted Shiite pilgrims headed to the holy Shiite city for Arbaeen, one of the most sacred days in the Shiite Muslim religious calendar.
The officials initially said the blast -- 200 meters from the Imam Hussein Shrine -- was caused by a bomb left in a garbage container, but Interior spokesman Maj. Gen. Abdul Karim Khalaf said authorities were looking into reports that a suicide bomber launched an attack.
Such attacks are signs that the sectarian conflicts that devastated Iraq in recent years are not over.
On Wednesday, a double car bombing struck a Baghdad bus station where Shiite pilgrims gathered for Arbaeen. Sixteen people were killed and 43 were wounded. Also, two pilgrims were killed and 16 were wounded Wednesday in roadside bombings in Baghdad.
Arbaeen commemorates the end of a 40-day mourning period for Imam Hussein, the grandson of the Prophet Mohammed and one of the most revered Shiite figures. He died in battle in the seventh century and is buried in Karbala.
In recent years, insurgents have targeted Shiite pilgrims, who usually walk to Karbala from across Iraq as a demonstration of piety and as part of tradition. The city is about 60 miles (100 km) southwest of Baghdad.