Iraqi officials say a bomb blast killed at least eight Shi'ite pilgrims Thursday as they observed one of their most important religious holidays.

More than 50 others were wounded in the attack that took place near the Imam Hussein shrine in the holy city of Karbala.

There were conflicting reports of whether the explosion was due to a roadside bomb or a suicide bomber.

The violence follows a twin bombing that killed 16 people near a bus station in Baghdad Wednesday. That blasts happened as Shi'ite pilgrims traveled to Karbala.

The attacks took place despite increased security.  Authorities have set up checkpoints on routes into the central Iraqi city.Pilgrims are gathering in Karbala, about 80 kilometers south of Baghdad, for the annual Shi'ite religious ceremony of Arbaeen on Monday. 

The ceremony marks the end of the 40-day mourning period following the anniversary of the death of Imam Hussein, grandson of the Prophet Muhammad, in the seventh century A.D.The United Nations special representative in Iraq Staffan de Mistura Wednesday condemned the violence as "murderous" attacks "clearly designed to provoke sectarian tensions."

Also Thursday, police said a car bomb in Mosul killed four policemen and wounded at least three other people, including two civilians, the latest in a string of attacks in the northern city.

Although overall levels of violence in Iraq are down this year, Shi'ite pilgrims have frequently been targeted by bombings, with most of the attacks blamed on Sunni extremist militants.

Some information for this report was provided by AFP, AP and Reuters.