A UK spy plane sent to help search for more than 200 girls abducted by militant Islamists in Nigeria has developed a technical fault.
It has been forced to land in Senegal for repairs, the Ministry of Defence said.
The plane left the UK on Sunday, joining an international effort to secure the release of the girls.
The Boko Haram group captured the girls from their boarding school in Chibok town in north-east Nigeria on 14 April.
The US military is flying manned and unmanned surveillance aircraft over Nigeria to look for the girls, Reuters news agency reports.
Israel says it has sent intelligence experts and specialists in hostage negotiations to help with the rescue effort.
The BBC's Will Ross in Nigeria says the plane's breakdown is a set-back for the UK government which promised to do all it can to help with the search operation.
Boko Haram says it is prepared to free some of the girls in exchange for the release of its fighters and relatives being held by Nigeria's security forces.
Nigeria's government says it is prepared to hold talks with Boko Haram, but has reportedly ruled out a prisoner swap.
On Sunday, a suicide blast in a street full of bars and restaurants in the northern Nigerian city of Kano killed four people.
Officials blamed Boko Haram for the explosion.
More than 1,000 people have been killed in Boko Haram attacks this year but the government has said it has pushed the militants back into their strongholds in the north-eastern Borno state.
This is where they seized the school girls, causing international outrage.
African leaders meeting in Paris at the weekend agreed to wage "war" on Boko Haram, pledging to share intelligence and co-ordinate action against the group.
The group is fighting to overthrow the Nigeria government and create an Islamic state.
But it has often attacked Muslims, including preachers who disagree with its interpretation of Islam.
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