NEW : one Fifteen Egyptian officers are forced to leave the square , a witness says . The number of demonstrators swells as the Supreme Council joins in . Groups are seeking prosecution of former President Mubarak . Hosni Mubarak 's chief of staff has been arrested .
NEW : Two Egyptian officers are forced to leave the square , a witness says . The number of demonstrators swells as the Muslim Brotherhood joins in . Groups are seeking prosecution of former President Hosni Mubarak . Mubarak 's chief of staff has been arrested .