Sudanese government forces have launched a massive offensive in three southern provinces, displacing hundreds of thousands of civilians, according to Sudanese rebels.
Southern Peoples Liberation Movement spokesman, Samson Kwaje, said that mechanised infantry columns supported by helicopter gunshops began attacking rebel-held villages in Bahr-el-Ghazal and Western and Eastern Upper Nile provinces on Saturday.
He said heavy fighting is taking place along a road connecting the government held-town of Wau and rebel-held Gogrial, 1,000 kilometers southwest of the capital, Khartoum.
"It is very serious. They came out of Wau town. They are heading towards Gogrial. They have also come out of Wau towards Tonje. As they were coming out of Wau, they were attacking villages, and they were burning villages," Mr. Kwaje said.
He said hundreds of thousands of civilians have been driven out of their homes. He has said that this has "created a humanitarian catastrophe of the highest scale, reminiscent of the 1998 famine."
The government of Sudan denies these allegations.
Mohamed Dirdeiry, a senior official at the Sudanese embassy in Nairobi has charged, if the SPLA has any serious allegations it should first file them with concerned international bodies who can look into them.
But aid agencies are backing up the rebels claims.
Paul Savage of Christian Aid said an attack on Gogrial has long been anticipated. He said there has been a government of Sudan military build-up in the area earlier this month.
"I was in Mapel which is southwest of Wau at the beginning of the month. There were stories on the ground that the GOS - they kind of test things out a little bit, before they actually do anything. There was a build up of horseman militia in Wau and they had been going up and down the road to a place called Acumcum which is on the way towards Gogrial. Just testing out the ground really. I think to see how strong the SPLA were in the area," Mr. Savage said.
Observers believe the government of Sudan wants to recapture Gogrial before the end of the dry season. This would improve government supply lines and offer better protection for their oil fields which are under rebel attack.
However, Mr Savage believes the SPLA's estimate of the number of civilians displaced by the offensive is inflated.