Boko Haram, which kidnapped 110 schoolgirls in Dapchi, northeast Nigeria, just over a month ago have so far returned 101 of the students to the town, the government said on Wednesday.
Information Minister Lai Mohammed said the girls were released "unconditionally". "No money changed hands," he told reporters in the capital, Abuja.
He added: "As of now, the number [of girls confirmed to have been released] has increased to 101."
Fatima Gremah, 13, who was among those released, earlier told reporters: "Boko Haram said we were lucky we were young and also Muslims.
"One of us who is a Christian has been left behind. They said they would keep her until she converted.
"If she converts, they will release her. She is the only one among us left behind."
Nigeria's President Muhammadu Buhari said last week the government had "chosen negotiation" to secure the return of the Dapchi girls rather than use military force.
Mr Mohammed had earlier said their release was the result of "back-channel efforts" with the help of "some friends of the country", without elaborating.
Military operations in and around Dapchi had been suspended "to ensure free passage" of the girls and also to ensure "that lives were not lost", he added.
Nigeria's presidency said separately the girls were in the custody of the country's intelligence agency, the Department of State Services.
Aisha Alhaji Deri, a 16-year-old student who was among those kidnapped in Dapchi, told reporters they were not mistreated during their time in captivity.
But she added: "When we were being taken away, five of us died on the way.
"They brought us back this morning, dropped us outside the motor park and said we should all go home and not go to the military because they will claim to have rescued us."
Fatima Gremah and another girl, Amira Adamu Mohammed, 16, both also said they were not mistreated and were given food to cook.
Fatima indicated they were held on an island on Lake Chad, which is a known stronghold for fighters loyal to Boko Haram factional leader Abu Mus'ab Al Barnawi.
"They just told us on Saturday to get onto boats. We spent three days on the water before coming to shore, then they put us in vehicles and said they were taking us back home."
Parents earlier said the girls were brought back to Dapchi in nine vehicles at about 8am. Some of the students headed to their homes in surrounding villages.
Bashir Manzo, who heads a parents' support group in Dapchi, said: "These girls were not accompanied by any security personnel.
"Their abductors brought them, dropped them outside the school and left, without talking to anyone."
Parents in the remote town said the girls had been taken for medical check-ups after their ordeal.
Boko Haram has used kidnapping as a weapon of war during its nearly nine-year insurgency which has claimed at least 20,000 lives and made more than two million others homeless.
The ISIL affiliate has not claimed responsibility for the abduction but given the location, Barnawi and his fighters have been blamed.
In August 2015, ISIL publicly backed Barnawi as leader of Boko Haram, or Islamic State West Africa Province, over Abubakar Shekau, whose supporters carried out the Chibok abduction.
Analysts have attributed a financial motive to the Dapchi kidnapping given government ransom payments made to Boko Haram to secure the release of some of the captives from Chibok.
On Tuesday, Amnesty International claimed that the military ignored repeated warnings about the movements of Boko Haram fighters before the kidnapping.
The military rejected the allegation, calling it an "outright falsehood".
Similar claims were made about the hours leading up to the abduction of 219 mostly Christian girls from Chibok, which brought sustained worldwide attention on the conflict for the first time.
The Chibok abduction also triggered a global campaign for their release, spearheaded by the US former first lady Michelle Obama.
There was no similar campaign for the Dapchi girls.
Since May 2016, 107 Chibok girls have escaped, been found or been released as part of a government-brokered deal with the jihadists.