Neighbours of the Democratic Republic of Congo have been warned not to interfere in the crisis there.
Some 36,000 people have fled the recent unrest
Fearing a regional war could reignite, the 15-member UN Security Council has told Rwanda, Uganda and Burundi not to back armed groups in DR Congo.
DR Congo has accused Rwanda of backing renegade forces which briefly took control of the eastern town of Bukavu.
The unrest threatens DR Congo's peace, following five years of war, in which all three countries were involved.
Three million died during the war which sucked in at least six other countries, including Rwanda and Uganda who backed rebel groups.
"The Security Council underlines that any attempt to disrupt the peace and transition process in the Democratic Republic of Congo, including through support for armed groups, will not be tolerated," the Security Council said in a statement.
It particularly called on Rwanda not to provide practical or political support to armed groups and instead to use its influence to de-escalate the current crisis.
The Congolese government is reported to have deployed some 10,000 troops near the border with Rwanda, which has twice sent troops into DR Congo in recent years.
US and UK envoys have gone to DR Congo and Rwanda to try and calm tensions in the region.
US envoy Donald Yamamoto was in the Rwandan capital Kigali on Wednesday to meet President Paul Kagame, after holding private talks with President Joseph Kabila of DR Congo the previous day in Kinshasa.
Meanwhile, junior UK government minister Chris Mullin held discussions with former rebel leaders Azarias Ruberwa and Jean-Pierre Bemba, who are both vice presidents in the Congolese power-sharing government set up under last year's peace deal.
Mr Yamamoto said the US preferred to use "diplomatic persuasion" not "threats" to find a resolution.
"We're trying to go beyond the rhetoric... and to ease the rhetoric and just stick to what the facts are," Mr Yamamoto told the BBC's Focus on Africa programme.
One of the men who took control of Bukavu, Colonel Jules Mutebusi, on Tuesday fled to Rwanda, along with 305 men, who Rwanda says were disarmed.
DR CONGO'S WAR
Seven foreign armies
At least 3 million dead
Disease and abuses widespread
Rwanda says it accepted them, as it would any people feeling fighting "under international conventions".
South African President Thabo Mbeki described the possibility of war between DR Congo and Rwanda as "potentially catastrophic".
The UN has some 10,000 peacekeepers in mineral-rich DR Congo, but they have been unable to stop the fighting.
The Security Council urged the heads of neighbouring state to work together to restore confidence in the region and said DR Congo should facilitate humanitarian assistance for Congolese refugees who had fled to neighbouring Burundi.
Many humanitarian and aid agencies have already pulled out of DR Congo, according to the BBC's Rob Walker.