KHARTOUM, June 23 (Reuters) - Sudanese President Omar Hassan al-Bashir said Africa's largest country had agreed with neighbouring Chad to disarm militias on both sides of the border, a semi-official news service reported on Wednesday.

Fighting broke out last year in the western Sudanese region of Darfur, which borders Chad, forcing hundreds of thousands of people to flee their homes and triggering what the United Nations calls the world's worst humanitarian crisis.

Two rebel groups launched an uprising in February 2003 accusing the government of neglect and of arming Arab militias to loot and burn African villages.

The Khartoum government denies the charge, saying that the Arab militia groups, known locally as Janjaweed, are outlaws.

"We have completed an agreement with Chad to collect arms in Darfur and the Chadian lands neighbouring Darfur at the same time," Sudanese Media Centre reported Bashir as saying on Tuesday during a meeting with invited journalists.

"To disarm the groups in one area without the other would not help in resolving the problem," Bashir said.

Chadian President Idriss Deby's adviser on foreign affairs warned last week that Sudan's inter-tribal violence could spill over the border and said the Janjaweed had been seeking the backing of Chad's Arab tribes.

Aid workers say about 158,000 refugees from Darfur have fled into Chad. Humans rights groups, aid agencies and refugees have said that Janjaweed, with government support, have crossed several times into Chad to attack local villagers and refugees.

Bashir ordered "a complete mobilisation" to disarm all illegal armed groups in the Darfur region on Saturday, including the Janjaweed, who have been accused of burning African farming communities to the ground to drive away villagers.

The government and the rebel groups signed a truce with the government on April 8, but each side has since accused the other of truce violations.