By Patrick Worsnip

TRIPOLI, Sept 9 (Reuters) - The U.N. Secretary-General said on Sunday he was encouraged by the "credible progress" he felt had been made towards peace in Darfur during an Africa tour, but it was too early to talk of tangible results. Ban Ki-moon said the challenge now was to persuade all Darfur's rebel groups to attend talks with the Sudanese government next month, he told international news agencies in an interview at the end of his trip to Sudan, Chad and Libya.

He called upon key regional countries to help produce a "road map" on the way ahead in the seven-week run-up to peace talks, to which Khartoum agreed in a statement issued during Ban's visit on Thursday.

The talks are scheduled to start on Oct. 27 at a venue in Libya, yet to be decided.

"I think we have made a lot of credible progress at this time towards the path to peace and security in Darfur," Ban said. "I am encouraged by this progress."

"But we must build upon this progress," Ban said.

"It is too early to say that we have made some good achievement."

In his eight and a half months in office, Ban has made solving the Darfur crisis a top priority.

International experts estimate that some 200,000 people have died and over 2 million have been made homeless since a rebellion broke out in the west Sudanese region in 2003.

Much of the killing, rape and looting has been blamed on a government-allied militia known as the Janjaweed.

Sudan denies the charges and says only 9,000 have died as a result of the uprising.

REBEL SCEPTICISM

Some of the eight or so Darfur rebel groups seen by U.N officials as significant players have already reacted with scepticism to the announcement of the talks, saying they expect little to come of them.

One rebel leader has said he will not attend because a planned international peacekeeping force will not be in place in Darfur by then.

Ban urged key regional countries -- which U.N. officials identify as Sudan and neighbours Chad, Egypt, Eritrea and Libya -- to work closely with the United Nations ahead of a high level meeting on Darfur which he will chair in New York on Sept. 21.

The talks in Libya will be mediated by U.N. special envoy Jan Eliasson and his African Union counterpart Salime Ahmed Salime, who Ban said would be touring the region and seeking to contact leaders of rebel groups.

Libyan leader Muammar Gaddafi told Ban at a meeting on Saturday that he too would try to assemble as many rebel groups as he could.

But in a potential obstacle to the talks Paris-based Abdel Wahid Mohamed el-Nur, founder of the Sudan Liberation Movement, has said he will not come to Libya. In reply to a question, Ban said: "He should look at the reality".

U.N. officials have hinted the Libyan talks may continue until an outcome is achieved.

The 26,000 strong U.N. and AU peacekeeping force, approved by the U.N. Security Council in July, is not expected to deploy before next year, except for a few small advance parties. But some human rights groups and aid organisations have questioned whether its mandate will be strong enough to protect civilians against any future violence.

Ban declined to go into the force's precise rules of engagement, but said he had urged Sudanese President Omar Hassan Al-Bashir, whom he met twice in Khartoum, that he must cooperate fully in order to enable the force to deploy.

"He must keep the cessation of hostilities," Ban said.

"He must not do any further aerial bombardment, he must ensure a smooth flow of humanity assistance to protect humanitarian workers."

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