By Ishbel Matheson BBC, Western Upper Nile

Tens of thousands of people are fleeing fighting in Sudan's oil-rich region of Western Upper Nile, following the fall of the key rebel-held town of Mankien to government forces in June.

The charity Christian Aid says there is clear evidence that civilians are being targeted in the government offensive.

The war in Sudan between the Islamic government of the north and rebels from the mainly Christian south has lasted nearly two decades, and despite recent US efforts, it seems to be getting worse, with terrible consequences for civilians.

Men, women and children are driving livestock before them in search of a place of safety.

Mosquito-infested

They carry only a few cooking pots and straw mats.

Families are now camping out in the open in mosquito-infested swamps.

Civilians are the first victims of the war

They have no protection against the heavy downpours of Sudan's rainy season.

The children are falling sick.

Cows are the main source of wealth and food for these pastoralist Nuer people, but the carcases of calves and cows now lie on the open plains.

Low-flying

Those who lived closest to Mankien talk of attacks by helicopter gunships and Antonov bombers.

Two boys showed me injuries they said had been caused by bullets fired at them from the helicopters.

They said the aircraft were so low they were skimming across the tops of the grass huts.

Government forces are stepping up the pressure on the SPLA

On Friday last week there was more mayhem as government militias broke through the rebel lines again, attacking and looting villages south of Mankien and causing more villagers to flee.

The United States Government recently brokered a deal between the SPLA rebels and the Khartoum government where both sides agreed not to target civilians.

In Western Upper Nile, that deal is being blatantly violated.