Around 40 students from an army-run boarding school were still believed to be in Taliban captivity on Wednesday, one day after the military said all those kidnapped had been rescued, officials said.
"More than 40 students and two teachers are still missing. Militants have abducted them," the top administration official in the northwest town of Bannu where the students had been headed, Sardar Mohammad Abbas, told AFP.
Tribal elders were mediating with the militants to secure their release, the commissioner said.
A convoy of about 30 vehicles carrying staff members and students from the college in northwest Pakistan at the start of the summer holidays was ambushed and busloads of people were abducted on Monday, government and military officials said.
Pakistan's military said on Tuesday it had recovered 80 students and staff when militants moved them from North Waziristan to South Waziristan -- lawless tribal zones on the Afghan border where Al-Qaeda is known to be active.
But staff of the college at Razmak in North Waziristan confirmed on Wednesday that more than 40 students and two teachers were unaccounted for.
"According to my information, 45 students and two teachers are missing. The college administration is monitoring the situation. We are trying to trace and recover them with the help of local people," spokesman Javed Alam told AFP.
"Forty-five students and two teachers are missing, they are in the Taliban custody," Fazal Khaliq, one of the college teachers, told AFP by telephone.
Taliban spokesmen were unavailable for comment and no militant group has yet claimed responsibility for any such abduction.
A senior security official handling the affair told AFP that so far no demand had been made for the release of up to 42 students and two staff.
A convoy of about 29 vehicles left the college. Eight were impounded by the Taliban and the rest escaped to safety on Monday, the official said.
Six vehicles of 80 people were rescued by the military on Tuesday and two buses of around 40 to 45 people remain in militant custody with tribal elders from North Waziristan trying to negotiate their release, he added.