Baghdad: Officials say a bomb on a parked motorcycle exploded on the outskirts of the holy city of Karbala, killing at least 10 Shiite pilgrims and wounding around 25 others.

The blast was the latest in a string of attacks this week that have targeted pilgrims making their way to an important Shiite religious observance in Karbala, raising fears of a spike in attacks when the pilgrimage culminates Friday.

The official said the bomb exploded at about 11 am in an area known as Ibrahimia, near the east entrance - one of three - into Karbala. The city is located 50 miles (80 kilometres) south of Baghdad.

The official, who spoke on condition of anonymity because he was not authorised to release the information, said at least 25 people were wounded in the attack.