ADDIS ABABA, July 4 (Reuters) - Sudan has started disarming Arab militias accused of sowing death and terror in its western region of Darfur and is confident the process will proceed smoothly, Foreign Minster Mustafa Osman Ismail said on Sunday.

"It is under way," Ismail said, following his government's pledge on Saturday to disarm the Arab "Janjaweed" fighters responsible for uprooting more than one million people and creating what the United Nations has called the world's worst humanitarian crisis.

But rebels said the operation was a cover for preparations for a new wave of ethnic cleansing. They said a large government force was being mobilised in the regional capital.

Ismail said a joint commission agreed during last week's visit to the region by U.N. Secretary General Kofi Annan would verify the disarmament of the militia.

"We are making real progress," he told Reuters.

The Darfur crisis has taken centre stage ahead of this week's summit of the African Union (AU) in Addis Ababa, where on Sunday the top AU official warned that Sudan faced a worsening humanitarian crisis unless the militias were stopped.

Najeeb al-Kheir Abdul Wahab, Sudan's state minister for foreign affairs, said police and army units were conducting the disarmament.

"We have collected weapons by force," Wahab said. "The process of general and complete disarmament is under way under effective government control."

Sudan's promise has been greeted with scepticism by some human rights groups, which have joined U.S. officials in accusing the militia of carrying out ethnic cleansing campaign against black Africans.

Underlining that scepticism, the rebel Sudanese Liberation Movement
(SLM) said it feared Khartoum planned a new offensive from Nyala, the capital of Southern Darfur state.

"The movement knows that under the cover of what is being termed 'the disarmament of the Janjaweed', the government is preparing a new ethnic cleansing push after the mobilisation of a large force from Nyala," the SLM said in a statement.

The SLM is one of two main rebel groups in the remote region, where Arab nomadic tribes have traditionally vied with African farming communities for scare resources.

The rebels accuse the government of neglecting the poor region and arming the Janjaweed to loot and burn African villages, a charge Khartoum denies.

Some 10,000 to 30,000 people are estimated to have been killed in Darfur, and the United Nations has said two million people have been caught up in the fighting. About 200,000 refugees have fled to neighbouring Chad.

TALKS VENUE ROW

AU head Alpha Oumar Konare said all sides in the Darfur crisis had agreed to meet at the AU headquarters in Addis Ababa on July 15. But Sudanese officials in Khartoum said peace talks should be held in Chad, where a ceasefire with rebels was reached in April, not Ethiopia.

"Negotiations need to be in N'Djamena," Sudan's ruling National Congress Party Secretary-General Ibrahim Ahmed Omar told the Sudan Media Centre news agency on Sunday.

The two main Darfur rebel groups said they would only take part in talks once the Janjaweed had been disarmed.

The rebel Justice and Equality Movement (JEM) also said it would not take part unless the government abided by the April truce. Both sides have accused the other of violations.

(Additional reporting by Opheera McDoom and Nima Elbagir in Khartoum.