KHARTOUM/JUBA: Fighting has broken out between government forces and rebels in central Sudan, both sides said on Sunday, in an escalation of violence so far concentrated closer to the country's borders.

Justice and Equality Movement (JEM) rebels from the western Darfur region said they attacked troops in North Kordofan state.

Fighting with the army has been so far mainly limited to Darfur as well as South Kordofan and Blue Nile states bordering South Sudan, which seceded from Sudan in 2011.

The state of North Kordofan is closer to the Sudanese capital Khartoum and a large producer of gum arabic, a substance extracted from acacia trees used by the food and drinks industry and an important source of earnings for cash-strapped Sudan.

JEM said it had seized the western area of Wad Bahr in North Kordofan from government forces on Saturday. "We beat the army and seized many weapons," JEM spokesman Gibril Adam said.

JEM and two other Darfur groups formed an alliance with rebels from southern Sudan, the SPLM-North, in 2011 to try to topple veteran President Omar Hassan al-Bashir.

Authorities confirmed the fighting but said the army and security forces repelled rebels trying to "steal from citizens", according to the state-linked Sudanese Media Center (SMC).

"They suffered heavy losses," North Kordofan's governor Muattasim Mirghani told SMC, adding that the army had destroyed 12 rebel vehicles.

Army spokesman al-Sawarmi Khalid said the rebels entered Sudan via the border with South Sudan, state news agency SUNA said. "The army had monitored their movement," he said.

Sudan accuses South Sudan of supporting the rebel alliance, a claim denied by Juba. The countries' disputes over border territory and oil rights almost led to war last year.

South Sudan's army accused Sudan of sending militias into the disputed region of Abyei, where fighting broke out in 2011 and peacekeepers monitor a ceasefire.

"Villagers continued to be harassed and attacked by the pro-Khartoum government ... militia," South Sudan army spokesman Philip Aguer said late on Saturday.

"More than 200 cattle and more than that number of goats have been looted by the same militia," he said.

There was no immediate comment from Sudan.

In September, the African neighbours agreed to end hostilities and restart cross-border oil flows, the lifeline for both their battered economies.

But neither has withdrawn armies from the poorly-defined border as agreed. Decades of civil war ended with a peace deal in 2005 and paved the way for southern secession.

Fighters of the Sudan People's Liberation Movement-North (SPLM-North) sided with the south during the civil war and now complain, like the Darfur rebels, of marginalisation in Sudan.