The military says the use of force could get the hostages killed, but the president, Goodluck Jonathan, has reportedly ruled out demands for a prisoner exchange.
Defence chief Air Marshal Alex Badeh announced last night that the military had located the girls, but offered no way forward.
"We can't go and kill our girls in the name of trying to get them back," he said.
Previous military attempts to free hostages have led to prisoners being killed by their abductors, including the deaths of a British and an Italian engineer in northern Sokoto town in March 2012.
A human rights activist close to mediators said that a swap of detained extremists for the girls was negotiated a week ago but fell through because President Jonathan hadcategorically refused to consider a prisoner exchange.