NAIROBI, APr 22, 2005 --The first United Nations troops have started arriving in south Sudan to enforce a peace deal signed in January ending 21 years of civil war.

Meanwhile, in Nairobi attempts to reconcile warring militias with the main rebel movement and the Khartoum government ended with an appeal for unity despite the absence of several key warlords.

Observers warned that without figures such as Gabriel Tanginya and Paulino Matip, who both command heavily armed militia blamed for abducting hundreds of civilians, reconciliation attempts would be worthless.

"If you had a mental list of militia leaders, you'd want them all there, and some of the big names are not there," said one UN official. "If I was the organiser, I would feel disappointed."

Two million people died and 4m fled their homes in the conflict between southern rebels and the Arab-dominated northern government.

The Sudan People's Liberation Army, the main rebel movement in the south, and Khartoum ministers signed a final peace deal this year.

But as many as 30 armed militias remain outside the agreement, making them a big threat to peace. A handful of their leaders attended the three-day conference organised by the Moi Africa Institute in Nairobi, with the majority represented instead by an umbrella body, the South Sudan Defence Forces.

The conference ended yesterday with the release of a joint statement saying that all sides would work towards reconciliation.

International donors promised $4.5bn (€3.4bn, £2.4bn) last week to kick-start development, but hundreds of thousands of refugees outside Sudan say they will not return until peacekeeping troops are deployed.