BAGHDAD, March 6 (Reuters) - A suicide bomber killed eight Shi'ite pilgrims and wounded 14 others south of Baghdad on Tuesday, one police source said. Another police source said two suicide bombers struck a group of pilgrims in the city of Hilla. Streams of Shi'ite pilgrims are heading to the holy city of Kerbala to commemorate a religious event. Sunni Arab insurgents have attacked Shi'ite pilgrims in the past.