The UN Security Council passed a French-drafted resolution on Wednesday saying it would consider sanctions against more M23 rebel leaders and "those providing external support", though it did not name any country.
This stance has been echoed by the United States, with Secretary of State Hillary Clinton making some of her toughest comments yet on the crisis, calling on the region's leaders to withdraw backing for the rebels.
The M23 rebel group – army mutineers whose rampant advance through eastern Democratic Republic of Congo has raised fears of wider conflict and humanitarian catastrophe – have pledged to leave Goma by the end of the week, presenting the government with a list of demands in return.
But while the rebels say they have already begun withdrawing, deputy UN spokesperson Eduardo del Buey said on Wednesday that the local UN mission in DR Congo "reports that there has not yet been any major movement by M23 out of Goma".
There were however "signs that the M23 are preparing to withdraw" in line with a deal brokered by African army chiefs, he said.
Residents had earlier said dozens of trucks carrying food and ammunition had left the North Kivu province capital.
Goma is the main city in the eastern Kivu region abutting Rwanda and Uganda, and has been the flashpoint for two past wars fought largely over control of its vast mineral wealth, including copper, diamonds, gold and the key mobile phone component coltan.
Threat of sanctions
Rwanda and Uganda played active roles in back-to-back conflicts from 1996 to 2003, and the UN has accused them of supporting the M23 – a charge both countries deny.
The UN on Wednesday repeated its call for an end to foreign interference, backing it up with the threat of sanctions as demanded by the DR Congo government.
US Secretary of State Hillary Clinton also called on all regional African leaders to halt any support for the M23 rebels in the Democratic Republic of Congo.
Highlighting that 285 000 people have fled their homes since the rebels began their advance in eastern DR Congo in April and many were in "critical need", Clinton urged the rebels to cease attacks and withdraw from Goma.
"We call on leaders and governments from throughout the region to halt and prevent any support to the M23 from their territory," Clinton said.
"The humanitarian impact of this conflict in the eastern part of the country is devastating," she added after talks with the African Union chairperson Nkosazana Dlamini-Zuma at the state department.
The dramatic escalation in the uprising of the M23 has raised fears of a wider conflict and a new humanitarian crisis.
Rights groups and UN officials have accused the rebels of killing, raping and abducting civilians.A weekend summit of regional leaders called on the M23 to leave Goma, but also urged President Joseph Kabila's government to address their grievances.
'Plundered from top to bottom'
The Red Cross said Wednesday its workers had picked up and buried 62 bodies, including civilians, from the streets of Goma in the days after its capture.
The organisation reported civilians and combatants were criss-crossing the region in search of refuge and medical treatment, running short of food and unable to reach their fields.
DR Congo government spokesperson Lambert Mende charged that the rebels had plundered buildings in Goma "from top to bottom".
However life in Goma appeared more normal on Wednesday.
Shops were open, taxis were running and while there were a few rebels posted at junctions, their presence on the streets had been scaled down considerably.
M23 military commander Sultani Makenga said on Wednesday that the rebels were ready to pull back 20km outside Goma as pledged.
"Tomorrow morning, (the M23) will begin to move towards Sake, then Goma, to continue towards our original positions," said Makenga, who was personally hit with UN and US sanctions this month over allegations of atrocities including killings, rapes and abductions.
A Western military source has estimated the number of rebels in the North Kivu region at 1 500.
The government has ruled out any peace talks until the M23 quit Goma.
The M23 was founded by former fighters in an ethnic-Tutsi rebel group whose members were integrated into the regular army under a 1999 peace deal which they claim was never fully implemented.
They seized Goma last week in a rapid advance that the army proved unable to stop, despite backing from UN peacekeepers' attack helicopters.The complex web of rebel groups and militias battling for eastern DR Congo's mineral wealth has made the region chronically unstable. – Sapa-AFP