Nigerian army 'ignored school attack warning'

International security experts are arriving in Nigeria as efforts to rescue more than 270 missing schoolgirls are ramped up.

The military has rejected accusations that it was tipped off hours before Boko Haram kidnapped the girls.

Nearly a month after they were taken, more than 270 are still missing.

The Nigerian government has been criticised for being too slow to respond, and for rejecting earlier offers of international help.

Al Jazeera's Rawya Rageh reports from Abuja.