Iraqi officials say a bomb planted on a motorcycle exploded, killing at least 20 Shiite pilgrims near the outskirts of the holy city of Karbala.

The security officials said around 90 people were wounded in the blast that took place on Wednesday morning.

The attack was the latest in a string of bombings this week that have targeted pilgrims making their way to an important Shiite religious observance in Karbala.

The blasts have raised fears of a spike by suspected Sunni insurgents in attacks when the pilgrimage culminates on Friday.

The officials spoke on condition of anonymity because they were not authorized to brief the media.

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