Amnesty says Nigeria ignored warnings before schoolgirls' abductions
An international human rights group says Nigeria's military had advance warning of the attack on a school at which some 270 girls were kidnapped but failed to act.
Amnesty International says it was told by several credible sources that the military was given more than fours hours' warning of the raid.
Fifty-three of the girls escaped shortly after being seized on April 14, leaving more than 200 still captive.
The authorities have not yet commented on Amnesty's statement.
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