(Xinhua) At least eight civilians were killed and some 40 injured when a suicide bomber exploded his fuel tanker near a police headquarters in central Samarra in Salahudin province, the police said Sunday.'A suicide bomber driving a fuel tanker, rigged with explosives, tried to hit the heavily fortified police headquarters in Samarra, 120 km north of Baghdad, but failed to approach his target,' a police officer told Xinhua on condition of anonymity. The driver drove his tanker to a nearby market when fired upon by the security guards of the headquarters and blew it up, the source said. After the explosion, gunmen armed with rocket-propelled grenades and machine guns opened fire on the police guards outside the headquarters, but fled the scene after U.S. helicopter gunship came in aid of the police, he said.