Presidential challenger Buhari votes in Nigerian elections
Rebel Coalition Seizes Syrian Government-Held City of Idlib
Earth Hour in Asia
Offensive into Tikrit intensifies
Plane's co-pilot 'hid sick note on day of crash'
Saudi Arabia begins military campaign in Yemen
Explosion rocks New York City neighborhood
Co-pilot purposely crashed plane into Alps
Boko Haram fighters told to 'kill wives'