A Pakistani origin United States citizen doctor was killed by unidentified armed men here on Monday. According to police sources, Dr Mehdi resident of Chiniot came from US to Pakistan some days ago. He went to his parents' graveyard for offering fateha. Some unidentified armed men opened fire at him while he was returning to home, killing him on the spot. Police reached the spot and shifted the dead body to hospital for post-mortem. Police also started investigation.