Egypt : Three Egyptian officers forced to the square , witness protests . Numbers of demonstrators have swelled because the Muslim Brotherhood has joined . Groups are seeking prosecution of former president Hosni Mubarak . Egypt 's chief of police has been arrested .
NEW : Two Egyptian officers forced to leave square , witness says . Numbers of demonstrators have swelled because the Muslim Brotherhood has joined . Groups are seeking prosecution of former president Hosni Mubarak . Mubarak 's chief of staff has been arrested .