Sudan's president has promised to let sick Darfur rebel chief Suleiman Jamous travel abroad for medical treatment, United Nations (UN) Secretary General Ban Ki-moon told journalists in Khartoum on Tuesday.

Ban said President Omar Hassan al-Bashir had given him a personal pledge that Jamous would be released from effective house arrest as soon as possible. The promise was the strongest sign yet that Jamous could soon be allowed to travel.

"President Bashir agreed to his immediate release for medical treatment. Bashir said that Jamous would be taken to Kenya as soon as necessary arrangements had been made," Ban said in an impromptu news conference with journalists at the start of a six-day tour of Sudan, Chad and Libya.

"I appreciate President Bashir's kind gesture," Ban said, adding he had told the Sudanese president that releasing Jamous would "create a favourable atmosphere for the peace process".

Ban spoke as he was about to fly to the south Sudan capital of Juba to try to speed implementation of a 2005 peace deal that ended over two decades of fighting between north and south Sudan. Fighting has continued in Darfur.

Jamous, the Sudan Liberation Army's humanitarian coordinator, was the key liaison between Darfur insurgents and the world's largest aid operation helping some 4,2-million people in Sudan's war-ravaged west.

The UN had moved him to a UN hospital near Darfur more than a year ago without informing Khartoum. Sudan has called him a criminal and has said it would arrest him if he left UN care.

Jamous needs a stomach biopsy that cannot be performed in the UN hospital. Last week, he left the hospital for the first time in more than 13 months to walk to the nearby UN headquarters to ask to be flown out of Sudan for medical care.

The UN said Sudan had promised to allow Jamous to be released in August. But the rebel leader's supporters said no concrete moves were made to let him travel to Kenya for treatment.

The elderly Jamous is respected in Darfur and considered a consensus builder who could help peace efforts and unify fractured rebel groups.

International experts estimate that some 200 000 people have died and 2,5-million have been driven from their homes during four-and-a-half years of fighting in Darfur. The Sudanese government puts the number of dead at 9 000.