Twenty-one schoolgirls kidnapped by Islamist group Boko Haram more than two years ago have been reunited with their families.

The girls - some of whom were carrying babies - were placed in the custody of Nigeria's secret intelligence agency last week.

They've now been returned to their families in an emotional ceremony in the capital Abuja.

It's unclear how the release was negotiated, with authorities denying reports the girls were swapped for captured Boko Haram fighters.

An official says talks are under way to free the remaining captured girls, with almost 200 still missing.