Dar-Es-Salaam - Congolese refugees trickling into Tanzania this week spoke of a New Year massacre by rebels in which hundreds of civilians were killed, the Catholic aid agency Caritas reported yesterday. A priest who escaped the slaughter told Caritas of an attack on two villages south of the Congolese town of Uvira. He told them Mai Mai warrior tribesmen had killed a number of rebel troops in the area, but the rebels extracted a terrible revenge on the local population whom they suspected of aiding the Mai Mai.