NAIROBI, April 11 (Reuters) - Ugandan negotiators led by President Yoweri Museveni's younger brother have made significant progress at informal talks with Lord's Resistance Army (LRA) representatives on the Kenyan coast, mediators said.

Pax Christi, a Catholic peace group that is trying to push forward stalled negotiations between the two sides, said on Wednesday the March 31-April 6 meeting in Mombasa reached "significant agreements" on extending a truce.

"This week the LRA delegation will take the documents to their principals on the Sudan-Congo border to seek their approval," it said in a statement, referring to rebel leaders wanted by the International Criminal Court (ICC) for war crimes.

Two decades of fighting in northern Uganda have killed tens of thousand people and uprooted nearly 2 million more, creating one of the world's worst humanitarian crises.

Under a landmark truce agreed in August, LRA fighters were supposed to gather at two south Sudan camps -- one east of the Nile and one near the border with Democratic Republic of Congo.

Pax Christi said the Ugandan government team, led by Museveni's brother General Salim Saleh, agreed all LRA fighters would now be allowed to assemble at the western location.

It said agreement was also reached on policies to address what the rebels call the government's marginalisation of northern Uganda, and on giving a prominent role to traditional reconciliation rituals to make amends for years of atrocities.

Pax Christi said the government would ask parliament to pass laws recognising such "alternative justice mechanisms" and would then approach the ICC regarding the LRA indictments.

It gave no further details, but experts say the arrest warrants are a key sticking point since the rebels' top leaders refuse to leave their forest hideouts unless they are scrapped.

The ICC has called on U.N. peacekeepers in Sudan and Congo to arrest the wanted men. ICC chief prosecutor Luis Moreno-Ocampo has said Uganda's government was obliged to arrest and handover the LRA leaders.

Without senior LRA commanders sitting at the negotiating table in Juba, southern Sudan, the discussions stumbled along for months before effectively stalling in January when the rebels' representatives demanded a new venue and new mediators.

Uganda's government had said earlier this month it expected talks to resume in Juba this Friday after South Africa, Kenya and Mozambique agreed to join the process as mediators.

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