Twenty-one of more than 200 Nigerian girls kidnapped by Boko Haram from a school in Chibok in 2014 have been released after negotiations brokered by the Red Cross and Switzerland.
The International Committee of the Red Cross (ICRC) said in Geneva that it had "acted as an intermediary," without negotiating "as such" with the radical Islamist group.
"Today we transferred 21 of the Chibok girls and handed them to the Nigeria government authorities, acting as a neutral intermediary," an ICRC spokeswoman said.
Nigerian Information Minister Lai Mohammed denied reports that the girls had been swapped with four high-profile Boko Haram militants. "This is not a swap, this a release," he said, without commenting on whether a ransom had been paid.
The girls were due to "have some rest, with all of them very tired coming out of the process," presidential spokesman Mallam Garba Shehu said.
They were picked up by a military helicopter in the Banki area of north-eastern Borno state, the news website Sahara Reporters quoted a government source as saying.
They were first flown to the city of Kaduna and arrived Thursday in the capital Abuja, where they met Vice President Yemi Osinbajo after undergoing psychological and health exams, according to news reports.
A security source told Punch newspaper that the girls would be tested for HIV before being released to their families.
"These girls were taken away for more than two years now. They had lived with the criminals who thrive in drugs and all sorts of other things that are peculiar to criminals," the source was quoted as saying.
There was no confirmation for reports that many of the girls had given birth during their captivity.
"As I depart Abuja for Germany on an official visit, I welcome the release of 21 of our Chibok Girls, following successful negotiations," President Muhammadu Buhari tweeted.
The pressure group Bring Back Our Girls released the names of the girls.
“Following this development, we trust that our government will continue to work to keep the safety, security, and well-being of the other girls a high priority,” said the group, which campaigns for their release.
Boko Haram kidnapped 276 girls and young women on April 14, 2014, from their school dormitory in the north-eastern village of Chibok.
Only about 50 of the abductees managed to escape immediately.
Despite various attempts to search for the missing girls and to negotiate with Boko Haram, the military only managed to rescue one of the girls, in May.
The government came under strong criticism for its incapacity to rescue the girls who were being held as sex slaves or in forced marriages to Boko Haram fighters.
In August, the militant group released a video showing dozens of young women who the group claimed were the abducted pupils.
Boko Haram’s campaign to create an Islamic fundamentalist state has claimed at least 14,000 lives since 2009.