Nigeria's government has had indirect contact with the militants holding more than 200 schoolgirls, according to Sky News sources.

Intelligence sources say neighbouring countries Chad, Cameroon and Niger are using satellite imagery to help find the girls.

Sky's Correspondent Alex Crawford is in the Nigerian capital Abuja.

 The British Prime Minister has given his backing to the social media campaign calling for the abducted girls to be freed.

A picture has been tweeted of David Cameron holding a sign calling for them to be allowed to return home.

The U.S. first lady Michelle Obama and numerous celebrities have also been pictured with similar signs in recent days.