By Alexis Akwagyiram and Felix Onuah

ABUJA (Reuters) – Boko Haram has freed 21 of more than 200 girls kidnapped by the Islamist militant group in April 2014 in the northern Nigerian town of Chibok, the government said on Thursday.

Around 270 girls were taken from their school in Chibok in the northeastern Borno state, where the jihadists have waged a seven-year insurgency to try to set up an Islamic state, killing thousands and displacing more than 2 million people.

Dozens escaped in the initial melee, but more than 200 girls are still missing. The kidnapping brought outrage worldwide and their plight was promoted by a Twitter hashtag #bringbackourgirls.

“The release of the girls … is the outcome of negotiations between the administration and Boko Haram brokered by the International Red Cross and the Swiss government,” a presidency statement said. “The negotiations will continue.”

The presidency gave no details of the deal, saying only that the 21 girls were very tired and would first rest in the custody of the national security agency. They would then be handed over to Vice President Yemi Obinsajo, the statement said. President Muhammadu Buhari will travel to Germany on Thursday.

CNN published on its website a picture it said showed several of the freed girls, wearing veils and being escorted by soldiers in Maiduguri, capital of Borno state.

Authorities said in May one of the missing girls had been found and Buhari vowed to rescue the others.

In the past days, the Nigerian military has been carrying out a large-scale offensive in the Sambisa forest, a stronghold of Boko Haram, which last year pledged loyalty to the Islamic State militant group.

Boko Haram controlled a swathe of land around the size of Belgium at the start of 2015, but Nigeria’s army, aided by troops from neighboring countries, has recaptured most of the territory. The group still stages suicide bombings in the northeast, as well as in neighboring Niger and Cameroon.

Boko Haram published a video in August apparently showing recent footage of dozens of the kidnapped girls and said some had been killed in air strikes.

The militant group has kidnapped hundreds of men, women and children but the kidnapping of the Chibok girls brought it worldwide attention.

In the last few months Buhari has said his government was prepared to negotiate with Boko Haram over the release of the girls.

(Reporting by Alexis Akwagyiram, Felix Onuah and Ulf Laessing; Editing by Janet Lawrence)