Baghdad, June 23 (IANS) At least 71 prisoners were killed Monday when militants attacked a bus convoy transferring them to a**ther jail in Iraq's Babil province, a police source said. The gunmen attacked a convoy of buses carrying dozens of inmates from a prison which were escorted by the army unit of al-Aqrab Brigade in the provincial capital of Hilla, some 100 km south of Baghdad, to the one in the town of al-Qasim, the source told Xinhua on condition of a**nymity. It was **t immediately clear who killed these prisoners, the source said.