The Sudanese army has begun a massive operation to destroy rebel bases in northern Darfur, according to two factions based in the area.
The army is said to have launched the offensive in the town of Wadi Atron, near the Sudanese-Libyan border, on Tuesday and took control of areas which had for years been under the control of rebels who want more autonomy for the region.
Al-Sayyid Sherif, of the Sudan Liberation Army (Unity) faction, said: "They attacked our areas in Wadi Atron with a massive force.
"We consider this a new declaration of war."
SLA (Unity) is one of the largest Darfur rebel groups and was one of the few factions to say they were ready to go to peace talks.
A Sudanese army spokesman declined to immediately comment, but one army source confirmed there were operations under way.
Suleiman Marajan, a commander from the Sudan Liberation Army (SLA) faction, said: "They came with more than 200 vehicles and killed seven people."
The SLA was founded and is currently led by Abdel Wahed Mohamed al-Nur.
The oil factor
Marajan also said that the government had moved in Chinese workers who were looking for oil in the remote area.
The Dow Jones newswire news agency reported last month that state-owned Chinese oil service companies were in talks to help Sudan exploit crude reserves in North Darfur where security would be provided by the Sudanese army.
North Darfur is part of the so-called Block12A, a site where oil is said to have been found, and is operated by Sudan's state-owned Sudapet, Ansan, an independent firm, and Saudi Arabia's Al-Qahtani group, the article said.
The Sudanese oil ministry would not immediately confirm whether any exploration has begun in Block 12A.
Chinese companies dominate Sudan's budding oil sector which produces more than 500,000 barrels per day of crude.
In a related development, Luis Moreno-Ocampo, chief prosecutor of the International Criminal Court, told Al Jazeera that the ICC maintains its right to investigate human-rights violations in Darfur despite Sudan not recognising the ICC's jurisdiction.
He said that he had clear evidence of abuses committed in Darfur, including certificates for more than a hundred people, and a clear map of villages and regions that were exposed to attacks.
Ocampo described the violations that took place in Darfur as a "scandal".
According to the UN, up to 300,000 people have died and more than 2.2 million have fled their homes since the conflict erupted in February 2003.
Sudan says 10,000 people have been killed.
The war began when African ethnic minority rebels took up arms against the Arab-led Khartoum government and state-backed Arab militias.