By Pete Jones and Michelle Nichols
KINSHASA/UNITED NATIONS (Reuters) - Talks to end a two-year insurgency in eastern Congo stalled on Monday after the government rejected a call for amnesty for M23 rebel leaders as the United Nations expressed concern at a military buildup by the group around the provincial capital Goma.
Congolese President Joseph Kabila's government and the M23 rebels had agreed on two-thirds of a draft deal during recent talks in neighboring Uganda, U.N. special envoy to the Great Lakes region, Mary Robinson, told the U.N. Security Council.
"However, the parties found it difficult to agree on certain contentious and difficult issues that had remained problematic throughout the talks, namely the amnesty, disarmament and integration of M23," Robinson told the 15-member council.
"They have agreed to reconvene soon in order to overcome their differences," she said via video link from Addis Ababa.
During closed-door Security Council consultations after her public briefing, several diplomats said Robinson told them that Rwandan President Paul Kagame had conveyed a personal message to the M23 delegation to encourage them to reach a compromise.
U.N. experts have repeatedly accused Rwanda, the Democratic Republic of Congo's neighbor to the east, of supporting the M23 rebellion, a charge Kigali has robustly denied. Kagame did not respond to an immediate request for comment on whether he had contacted the M23.
Robinson visited Kagame in Kigali on Friday with envoys from the United States, the European Union and the African Union.
"The president believed that while the M23 was not Rwanda's issue, a peace agreement between the rebel group and the government of the DRC would benefit the entire region," she told the Security Council during her public briefing.
The Congolese government said it strongly opposed a blanket pardon for the commanders of the Tutsi-led rebellion and against reintegrating their fighters into the national army. M23 accused the government delegation of refusing to cooperate with its chief negotiator and of seeking a return to hostilities.
Martin Kobler, head of the U.N. peacekeeping mission in Congo known as MONUSCO, told the Security Council that in recent days "we have observed considerable military build-up on both sides of the front line."
"At the same time M23 has fired twice at unarmed U.N. helicopters and has strengthened offensive positions threatening U.N. peacekeepers," he said. "Information gathered indicates the M23 has also strengthened its frontline in the south near Goma."
M23 briefly captured Goma in November, then withdrew to pave the way for peace talks in the Ugandan capital Kampala. The rebellion's roots lie in the 1994 genocide in Rwanda, where Hutu troops and gangs killed 800,000 Tutsis and moderate Hutus.
'EXTERNAL INVOLVEMENT MUST STOP'
Eastern Congo has long been one of Africa's bloodiest battlefields. M23 emerged early last year when former rebel fighters - who were integrated into the Congolese army under a 2009 peace deal to end a previous revolt - staged a mutiny. The group takes its name from the deal on March 23, 2009, which fighters accused Kinshasa of not honoring when they deserted the army in 2012.
Kobler said that since the M23 rebellion began, the United Nations had sheltered nearly 200 combatants "who consistently and credibly claim to have been recruited on Ugandan but mainly on Rwandan territory."
"This and other kinds of external involvement must stop," he said.
The United States, which has called on Rwanda to drop its support for the M23 rebels, stepped up pressure on Kigali this month by moving to block military aid over the recruitment of M23 child soldiers in its territory.
Congolese forces, with the help of a new 3,000-strong U.N. Intervention Brigade that has a mandate to neutralize armed groups, successfully pushed M23 fighters away from Goma - a city of 1 million people - in August. The military defeat forced M23 to return to the Kampala peace talks.
Congolese government spokesman Lambert Mende said on Monday there was total disagreement over the amnesty proposed for M23 fighters, while M23 said in a statement that it was waiting for another round of talks to be organized so the remaining points of disagreement could be discussed.
Robinson said that in the draft deal under negotiation, amnesty and integration would be granted to all M23 members except those indicted for suspected war crimes, crimes against humanity, acts of genocide or gross violations of human rights.
M23 combatants would have to make a written commitment to "refrain from acts of rebellion" and their amnesty would be automatically withdrawn if those pledges were violated, said Robinson, a former Irish president.
Reintegration into the Congolese army would be on a case-by-case basis and conditions would include swearing allegiance to the state and constitution of the Democratic Republic of Congo and committing to serve in any part of the country, she said.
Robinson told Rwanda's Kagame that a peace agreement between M23 and Kinshasa "will enable the Force Intervention Brigade to deal with other armed groups in eastern DRC including the FDLR and the ADF."
Rwanda and M23 have accused the Congolese army of collaborating with the Hutu-led Democratic Forces for the Liberation of Rwanda (FDLR), an accusation Kinshasa rejects. The ADF is the Islamist group Allied Democratic Forces, which Uganda says is linked to Somalia's al Shabaab.
(Editing by Angus MacSwan and Xavier Briand)