A military and a civilian militia source in Banki, near the Nigerian border with Cameroon, said "at least 80" girls were brought to the town late afternoon on Saturday.

"The girls are now lodged in the military barracks and will be flown to Maiduguri (the Borno state capital) tomorrow," the same source added.

In a statement late on Saturday night, the Nigerian government thanked Switzerland and the International Committee of the Red Cross for helping to release the girls after "lengthy negotiations." They were released "in exchange for some Boko Haram suspects held by the authorities" and would arrive in Abuja on Sunday where they would "be received by the president."

Shehu Sani, a Nigerian senator who had been involved in previous negotiations with Boko Haram, said the girls were mostly "in good condition" and that talks to secure their release had lasted for "almost three to four months."

The government would now look to securing the remaining abducted girls, Sani added.

About 21 girls who had been kidnapped in 2014 were released last October in a previous deal with the kidnappers brokered by Switzerland and the International Red Cross. A handful of other girls have either escaped or been rescued, but 113 still remained unaccounted for following Saturday's release.

Read more: Boko Haram victim tells DW of captivity of Chibok girls

Security sources in the town of Banki, in Borno state, said that the girls had been brought there for medical checks before being airlifted on Sunday to Maiduguri.

The personal assistant to Nigerian President Muhammadu Buhari, Bashir Ahmad, tweeted that "huge numbers" had been released.

Last month President Muhammadu Buhari said in a statement that the government was "in constant touch through negotiations, through local intelligence, to secure the release of the remaining girls and other abducted persons unharmed"

The government denied that it paid a ransom for the girls' release and said it had freed some detained Boko Haram militants in exchange for the girls.

For more than two years after the kidnapping there was no sign of the missing girls but the discovery of one of them with a baby in May last year fuelled hope. Two more girls who successfully escaped have also since been discovered.

Read more: Boko Haram insurgency weighs on minority Christians three years after Chibok

A campaign #bringbackourgirls has been active in seeking the girls' release and has gained the backing of former US First Lady Michelle Obama and Nobel Peace Prize laureate Malala Yousafzai. A campaign representative said that it was awaiting confirmation on how many girls had been released. "Our hopes and expectations are high as we look forward to this news being true and confirmed," the campaign said.

Boko Haram kidnappings

The kidnapping in April 2014 was one of the most high profile incidents in Boko Haram's insurgency in northeastern Nigeria. Extremists initially abducted all 276 girls in the remote Chibok boarding school, although around 50 successfully escaped just a few hours later.

Now in its eighth year, Boko Haram's insurgency has sought to create an Islamic caliphate in northeast Nigeria, as well as in the bordering regions of Cameroon, Chad and Niger. Militants have killed more than 20,000 people, forced over 2.5 million to be displaced and adbucted thousands of women, forcing them into sexual slavery or marriages with its fighters.

Experts also believe that Boko Haram also forces its kidnap victims into becoming suicide bombers.

Although the Nigerian government last year claimed to have "crushed" the militant group, its members have continued to carry out attacks.

On Friday, the US and Britain issued warnings that the Islamist group was planning to kidnap foreigners "along the Kumshe-Banki axis" in Borno state.

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dm/jm (Reuters, AFP)