The attack in Samarra left at least 28 people dead and wounded more than 20 others [Reuters]

At least 28 people have been killed and more than 20 others wounded in an suicide attack on Shia Muslim pilgrims near the Iraqi city of Samarra, according to police sources.

Women and children were reportedly among the victims of Saturday's bombing.

The attack, which targeted pilgrims on travelling on a bus, was the second suicide bombing this week near Samarra, a Sunni-majority city, about 100km north of Baghdad.

Jane Arraf, Al Jazeera's correspondent in Baghdad, said: "This attack appears to have been particularly daring.

"According to police sources, a suicide bomber managed to get on to a slowly moving bus that was heading out of a parking lot, filled with Shia pilgrims."

The AFP news agency quoted a police official and a hospital source as saying that "about 27" people were killed in the attack. The Reuters news agency reported police sources as putting the toll at 28.

Samarra houses the gold-domed shrine of Hassan al-Askari, a revered ninth century imam, which draws pilgrims from Iraq and round the world.

Saturday marked the annual commemoration of his death.

Eight people were killed and 30 wounded on Thursday when a suicide car bomber attacked a group of Shia Muslim pilgrims heading to the city.