Israeli anti-terrorism experts have joined the international effort to find the 223 schoolgirls abducted by Islamist militants in Nigeria.

The girls were kidnapped by Boko Haram fighters in Nigeria's northeast.

They were abducteed from their school dormitory in the town of Chibok, on April 14 four weeks ago.

Nigeria's President Goodluck Jonathan accepted an offer of help from Israeli Prime Minister Benjamin Netanyahu during a phone conversation on Sunday.

Mr Jonathan told Mr Netanyahu: "Nigeria would be pleased to have Israel's globally acknowledged anti-terrorism expertise deployed to support its ongoing operations."

Britain, the United States and France have already sent specialist teams and equipment to help Nigeria's military in the search concentrated in the remote northeast.

But Washington said US troops would stay out of any rescue mission.

France has called for African leaders to hold a summit focused on the issue.

During a visit to Azerbaijan's capital Baku, French President Francois Hollande said a summit on security in west Africa, could be held as early as this Saturday "if the countries agree".

He said: "I suggested, with Nigerian President Goodluck Jonathan, a meeting of Nigeria's neighboring countries."

Nigeria's government has come under criticism for responding too slowly to the crisis.

Boko Haram, are known for attacking schools, churches, government installations and, increasingly, civilians since 2009.