One policeman was killed and another five were wounded in an insurgent attack on a constitution referendum centre in Baquba northeast of Baghdad, hospital sources said Friday, according to DPA. The sources said gunmen attacked late Thursday a referendum centre in Al-Abbara region north of Baquba injuring one guard. The sources said when a police patrol arrived at the scene and Improvised Explosive Device went off killing one policeman and wounding another four. Iraq is to hold a referendum on a constitution Saturday, the first of the kind in decades.