Three Iraqi police forces were killed while one of the members of Sahwa, (or Awakening) forces was injured in an armed attack by unidentified gunmen in Samarra, southern Tikrit, 170 km north of the capital Baghdad, an Iraqi security source said on Monday. Unidentified gunmen driving two cars opened fire at a police center in southern Tikrit, killing three policemen and injuring one Sahwa member, who was stationed at a checkpoint near the police center, added the source. A security cordon was imposed around the scene of the incident, while the injured were rushed to nearby hospital to receive treatment, said the source.