WASHINGTON - Senior envoys from the United States, Britain and France were shuttling between regional capitals to seek a cease-fire in the Democratic Republic of Congo (DRC), the US State Department said on Monday.

Department spokeswoman Victoria Nuland said US Assistant Secretary of State for African Affairs Johnnie Carson and his British and French counterparts were meeting with presidents and senior officials of Rwanda, Uganda and DRC in an effort to promote "a peaceful, sustainable resolution to the conflict."

"The goal remains the goal that we outlined last Tuesday or Wednesday: We want to see a cease-fire," Nuland said at a regular news briefing, adding "We want to see a pullback to July lines".

The rebel M23 militant group took Goma, the capital of North Kivu province, last Tuesday, despite the presence there of a 1,500- strong UN mission known as MONUSCO.

Questions have been raised about whether the mission should have done more to prevent the rebels' invasion as it has another 6,700 "blue helmets" in the province.

Nuland cast her doubt as well, as Washington is a major supporter of MONUSCO.

"Clearly, you know, MONUSCO was not able to do what it was mandated to do, so I think among the things we need to understand better is how this relatively modest group of rebels was able to grab and hold territories, and what might be needed in terms of security and stabilization going forward," she said.

But she said time was not right now for changing the mandates of the UN mission. "I don't think we're there yet. We're at the stage of trying to figure out among the regional leaders what it's gonna take," she explained.

The M23 rebellion started in April when a militia that had been integrated into the DRC armed forces mutinied, and the militant group has since operated in the eastern part of the country that is rich in mineral resources.

The fighting has displaced hundreds of thousands of people and sparked fear of another large-scale war in the country.

Both the DRC government and the United Nations said the M23 rebels are being supported by neighboring Rwanda and Uganda, a charge both countries deny.