Libya will not be able to export oil through its two largest eastern ports before August, due to safety checks after a near year-long closure, a senior oil official said on Wednesday. The latest twist in a spiral of violence also casts a shadow over the vital deal two weeks ago to end the eastern blockade by federalist protesters of the last two facilities they held. Until April, the rebels were holding four out of five eastern ports, cutting off over half of Libya's export capacity. But an oil export return is proving slow and a full ramp up is already facing new obstacles with a fresh protest by oil guards at the port of Brega. At least 15 people have been killed in the capital and the eastern city of Benghazi since Sunday.