By Martin Dawes in southern Sudan

The BBC has obtained exclusive footage of a new atrocity in the civil war in Sudan.

In the latest incident, 14 children were killed when government air force planes attacked a school in the rebel-held part of the remote Nuba Mountains.

A Sudanese student, using a battered camera with a broken microphone, captured the scene immediately after the bombing.

One bomb fell close to a tree where a class was having an English lesson. Many of the pupils died along with the teacher.

The cameraman, Stephen Amin, said all he could hear was screams.

It was "a very harrowing experience ... because the amount of people on the ground and then also the voices of horror and so on was very sad", he said.

Planes return

Three bombs are said to have fallen within the school compound and, afterwards, people had to flee because the aircraft apparently came back, perhaps to take a look.

The wounded were taken to a hospital run by a German medical group. The dead were buried immediately.

Father Tom Tiscornia - a Catholic missionary who came on the illegal flight to the area - expressed his anger after speaking to survivors.

"To purposely drop bombs on an area where there's known to be children and a school, that is just evil."

He told me there were no military targets nearby.

"Oh, no, no military target. It was just a civilian target."

Remote battleground

Nuba is a remote area where rebels and government soldiers fight regularly. The young adults have known only war, and many lives have been lost out of sight.

The government of Sudan is currently on a "charm offensive" with the West.

Among other things, it wants investors for its potentially lucrative oil industry and it would rather people didn't know about what happens in places like this and the crimes that are committed.

Fighting between the Muslim government in the north and forces in the mainly Christian south has already cost around two million lives.