(Recasts with Fatah joining truce) GAZA, May 16 (Reuters) - Hamas called a unilateral Gaza ceasefire, effective 1700 GMT on Wednesday, and a Palestinian official said the rival Fatah faction was also holding fire. Previous attempts to stem a flare-up of internal violence that has killed at least 40 Palestinians fell apart within hours, and it was unclear whether this one would be different. "We will unilaterally implement a ceasefire from 8 this evening," said Hamas spokesman Fawzi Barhoum. A Palestinian official said that President Mahmoud Abbas, who leads Fatah, "gave orders to all security forces and Fatah men to cease fire immediately".
