Ugandan rebels have walked out of peace talks aimed at ending a 19-year conflict in which thousands of civilians have died, officials said Thursday. Lord's Resistance Army rebels said they were boycotting the talks with the government because of a heavy military buildup by the Ugandan army, a senior rebel leader said.

"The Juba peace talks are in grave threat and danger of failure due to the unfolding heavy military deployment of UPDF (Uganda People's Defense Forces) troops in Uganda, Southern Sudan and the Democratic Republic of Congo," Martin Ojul, head of the rebel team negotiating a peace deal with the government, told The Associated Press.

"Until these issues, which are of grave concern to us, are resolved, the negotiations with the Ugandan government are on hold," he added. Ojul said the LRA were committed to peace to end one of Africa's longest wars and said they had no other option but to walk out.

The rebels said they would review there position in seven days.

But Southern Sudan's vice president Riek Machar, who is the chief mediator in the peace talks, told the AP he expected the negotiations to continue.

He was holding talks with the LRA late Thursday to iron out their objections, he said by telephone from Juba, the southern Sudan capital where the peace talks are taking place.

Machar also dismissed claims that the Ugandan army deployed forces close to neutral assembly points across the border in southern Sudan where the rebels were supposed to gather as part of the truce. Ugandan Army Maj. Felix Kulayigye made the same denial.

The rebels' move is the second serious blow in two days to the ongoing talks.

On Wednesday, the Ugandan army accused rebels of violating the increasingly fragile truce, which was signed last month, by leaving the neutral assembly points.

The cease-fire calls for rebel fighters to gather in largely uninhabited areas across the border in southern Sudan, where they will be protected and monitored by the southern Sudanese military while a broader peace deal is negotiated.

The rebels denied they had left the neutral camps.

The LRA is notorious for cutting off the tongues and lips of innocent civilians, enslaving thousands of children and driving nearly 2 million people from their homes.

It was formed from the remnants of a northern Uganda rebellion that began in 1986 after President Yoweri Museveni overthrew a brutal military junta.

LRA leader Joseph Kony mixed politics with religious mysticism, declaring himself a Christian prophet fighting to rule this country of 26 million people according to the Ten Commandments.

U.N. officials estimate the LRA has kidnapped 20,000 children in the past 19 years, turning the boys into soldiers and the girls into sex slaves for rebel commanders.

The rebel leadership are wanted by the International Criminal Court for war crimes and crimes against humanity.

Earlier this year, the court pressed Uganda, Sudan and Congo to hand the rebel suspects over for trial. However, Museveni has said he will not implement the warrants as long as Kony's group negotiates peace.