SAMARRA, Iraq - A suicide bomber targeting Shi'ite pilgrims killed 28 people and wounded 24 near the Iraqi city of Samarra on Saturday, a police source said.

The attack was the second suicide bombing this week near Samarra, where Shi'ite pilgrims are commemorating the death of one of their 12 revered imams in 874.

"Women and children are among them," the police source at Samarra hospital said of the casualties of the attack.

Another police source said the attacker was a suicide car bomber who attacked a coach filled with pilgrims leaving Samarra after visiting the shrine, while a third police source said the explosion had been caused by a suicide bomber wearing an explosive vest.

On Thursday, eight people were killed and 30 wounded when a suicide car bomber attacked a group of Shi'ite pilgrims heading to Samarra, 100 km (62 miles) north of Baghdad.

Samarra is the home of the al-Askari mosque and shrine. Pilgrims travel there for ceremonies to mark the death of Hasan al-Askari, the 11th of the 12 imams.

Shi'ite pilgrims have been targeted frequently in recent years by a stubborn Sunni insurgency which is still capable of carrying out lethal attacks almost eight years after the US-led invasion that toppled Saddam Hussein.

Shi'ite religious events were banned under Saddam.

Overall violence has decreased in Iraq since the peak of sectarian warfare in 2006-7, but bombings and attacks still occur daily.

Dozens of people died in attacks on Shi'ite pilgrims last month near the holy city of Kerbala. At least seven people were killed and 78 wounded by three car bombs in the northern city of Kirkuk on Wednesday.