By Opheera McDoom

KHARTOUM, Jan 19 (Reuters) - U.N. and African Union envoys urged the parties to Sudan's Darfur conflict on Saturday to attend peace talks after rebel divisions and boycotts stalled progress towards negotiations.

Jan Eliasson and Salim Ahmed Salim, on their first trip since failed negotiations in October, said deteriorating relations and tensions between Sudan and its western neighbour Chad were also inhibiting the peace process.

"This is a challenge to see if there is political will to move ahead and I hope that the parties accept this challenge," U.N. envoy Eliasson told reporters after the one-week trip.

He said of the five main rebel groups, the envoys had guarantees from two that they would attend a meeting in about six weeks to unify their position ahead of renewed negotiations.

But the key Justice and Equality Movement (JEM) of Khalil Ibrahim -- the biggest military group -- and the populist Sudan Liberation Movement (SLM) led by Abdel Wahed Mohamed el-Nur were still putting difficult conditions on attending any talks.

Some of the rebels reject Libya as the venue, saying leader Muammar Gaddafi had made comments belittling their struggle for equal rights for the people of Sudan's remote west.

But the envoys said the process which began in the Libyan town of Sirte would end there although they did not rule out that interim talks could be convened in other locations.

ARREST WARRANTS

International experts estimate some 200,000 have died and 2.5 million have been forced from their homes in the five years of revolt in Darfur, which borders Chad.

Washington calls the violence genocide, a term European governments are reluctant to use and Khartoum rejects.

The International Criminal Court has issued arrest warrants for a government official and an allied militia leader accused of war crimes but Khartoum has refused to hand them over.

The envoys said deteriorating relations between Sudan and Chad would hinder the peace process.

"From our perspective it is in the interests of Darfur to have normalisation between the two countries," Salim added.

Sudan and Chad accuse each other of supporting insurgents intent on toppling their governments. Chad bombed targets in Darfur earlier this year, saying they were attacking Chadian rebel positions inside Sudanese territory.

(Editing by Ralph Boulton)

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