The United States expressed concern Monday that a "relatively modest" group of M23 rebels was able to seize ground in the eastern Democratic Republic of Congo, despite the UN peacekeeping presence.
State Department spokeswoman Victoria Nuland told reporters that Washington was not yet ready to call for the MONUSCO force to be given a tougher mandate, but made it clear US officials were disappointed by its performance.
"One of the things that we need to understand better is how this relatively modest group of rebels was able to grab and hold territory, and what might be needed in terms of security and stabilization going forward," she said.
The United Nations' MONUSCO force has around 17,500 troops in the Democratic Republic of Congo, but this month it was unable to prevent the M23 rebels from making a startling advance to capture the key eastern city of Goma.
UN helicopters did launch strikes on guerrillas in the bush, but the "Blue Helmets" stood aside as they advanced on the town, arguing that they could not take the lead in war-fighting when the DR Congo army had melted away.
Some have called on the UN force to be better armed and given a more robust mandate to enable it to take on the rebels directly in battle, but Nuland said of Washington's stance: "I don't think we're there yet."
But she added: "Certainly there's a concern that we are going to need an effective security force there, and that might need adjustments going forward.
"We are a big supporter of MONUSCO and it needs to be effective in securing the population, which is not currently the case."