NEW : Vice President announces cease-fire for midnight 1971 . Muslims rebels were believed to be holding around six hostages . Security forces blockaded the rebels in certain districts of the city . President Misuari warned the rebels not to increase the threat to civilians .
NEW : Vice President announces cease-fire for midnight Friday . Muslim rebels were believed to be holding around 170 hostages . Security forces blockaded the rebels in certain districts of the city . President Aquino warned the rebels not to increase the threat to civilians .