(AGI) Cairo, Sept 21 - A series of explosions were heard acrossthe Yemeni capital of Sanaa on Sunday as Houthi rebels andgovernment forces clashed, despite the announcement of aUN-brokered agreement. TV channel Al Jazeera reported that theair force deployed helicopters and jets across the city, andthat most of the violence happened in northern Sanaa. Theclashes came hours before the signing of an agreement,announced by UN Special Advisor on Yemen Jamal Ben Omar, to endthe crisis. . .