KHARTOUM, Sept 22 (Reuters) - A rebel faction, which recently captured a town in Sudan's western Darfur region, slammed the country's new coalition government on Thursday saying that only war would bring fair rule.

"The national unity government has deliberately excluded large sections of Sudanese society and ignored the existence of the many marginalised in Sudan," said a statement signed by Mahjoub Hussein of the Sudan Liberation Army (SLA).

The new coalition government, announced this week, was only possible after a January peace deal ended more than two decades of war between southern rebels and the Khartoum government.

Some southerners have said they were unhappy with the composition of the new cabinet.

"There is no possibility of any democratic transformation other than (through) armed struggle in Sudan," the SLA said.

Hussein also signed a statement on Tuesday that said the SLA had captured the town of Sheiria, which has around 33,000 refugees. More than 80 soldiers were killed.

The fighting took place as another faction of the SLA, and the second main Darfur rebel group, the Justice and Equality Movement (JEM), held peace talks with the government in Nigeria.

JEM and the SLA launched the rebellion against the previous government in 2003 complaining of official neglect and marginalisation. The rebels said the government armed nomadic militias who burnt and looted settled communities.

MINISTERS SWORN IN

Fighting died down in the region over the past year but has surged again in the last month. Banditry has become an obstacle to delivering aid supplies, relied upon by around 3 million people in Darfur, as law and order has collapsed.

Sudanese First Vice President Salva Kiir warned on Thursday that the fighting in Darfur could spill into southern Sudan.

"The war in Darfur can also filter to southern Sudan because as you know southern Sudan has borders with Darfur," Kiir told delegates at an anti-terrorism conference in Khartoum.

He said there was a danger of confrontation with SPLM forces if Sudanese troops followed Darfur rebels moving south with refugees. He did not elaborate.

In Washington, U.S. State Department spokesman Sean McCormack congratulated the Sudanese government on the appointment of a cabinet but voiced strong concern over reports of a new upsurge in violence in Darfur.

"The parties must end violence and cooperate closely with the African Union, which has our unequivocal support. We urge the parties to make rapid progress in the Darfur talks," he said in a statement.

The new government, described by some as a "humiliation" for the former southern rebels, faces the challenge of finding a political solution for the Darfur conflict.

The former ruling National Congress Party (NCP), which controls 52 percent of the new government, holds the critical defence, interior, finance and energy portfolios.

Most of the ministers of the new government were sworn in during a ceremony at the presidential palace on Thursday, Sudanese media with links to the NCP reported.