RIYADH (Reuters) - Saudi Shias staged another small protest in the kingdom's oil producing Eastern province on Wednesday, defying a ban on demonstrations, witnesses said. More than 100 mostly young men gathered in the main Shia city of Qatif on the Gulf coast to demand the release of prisoners they say are held without trial, witnesses said. There was a heavy presence of police in Qatif which is close to Bahrain, scene of large protests by majority Shias against their Sunni rulers. Shias have staged protests for about two weeks in the east of Saudi Arabia, mainly to demand the release of prisoners.