CAIRO - Seven people were killed and more than 15 wounded by a bomb on Friday in the Yemeni city Marib, east of the capital Sanaa, police told Reuters. It was not clear who planted the device which went off around midday in the heart of a crowded market where the narcotic leaf qat is sold, they said. Marib has most of Yemen's oil and gas fields and has long been a battleground between factions including local tribesmen, al Qaeda in the Arabian Peninsula (AQAP) insurgents and other militants, and government forces.