(adds Negroponte arrival, Chadian delegation)

By Michael Georgy

KHARTOUM, April 12 (Reuters) - Libyan and Eritrean military and security observers have been deployed at the border between Sudan and Chad, scene of recent clashes, a Libyan mediator said on Thursday.

"We agreed on positive steps and the presence of military and security observers on the border from Libya and Eritrea, and from Chad and Sudan, and right now some of them are there on the border," Ali Triki, Libya's envoy on Chad and Sudan, told a news conference.

He did not say when the observers were deployed or how many had been sent there.

"I believe the confidence between both countries will return to normality, and if they respect agreements then we will not even need observers," said Triki, Libyan leader Muammar Gaddafi's top adviser on African issues.

Triki said a Chadian delegation was due to arrive in Khartoum over the next few days in a bid to calm the situation.

Gaddafi has taken the lead in trying to broker peace between Chad and Sudan, which have traded threats and accusations since a clash on Monday when Sudan said 17 of its soldiers were killed.

Chad denied any deliberate assault on its eastern neighbour, but said its forces had clashed with Sudanese troops after crossing the border to pursue Sudanese-backed rebels it said were launching raids.

That incident marked a sharp flare-up of tension between the two oil-producing central African countries, which have seen their ties become increasingly marred by violence spilling over from the conflict in Sudan's Darfur region.

Both Sudan and Chad are resisting international efforts to deploy U.N. peacekeeping forces.

A late February summit hosted by Gaddafi to keep the peace between Chad and Sudan agreed "observation mechanisms" along the Darfur frontier.

Sudan has witnessed a flurry of diplomatic activity aimed at easing tensions with Chad, including a visit by South African President Thabo Mbeki.

The No. 2 U.S. State Department official, John Negroponte, arrived in Sudan on Thursday on a regional tour that will include Libya and Chad to press for solutions to the Darfur crisis.

Negroponte is expected to deliver a tough message from Washington on Darfur. Sudanese officials have said international pressure on Darfur will only deepen the humanitarian crisis.

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