GOMA, Congo -- Rebels in Congo believed to be backed by Rwanda postponed their departure Friday from the key eastern city of Goma by 48 hours for "logistical reasons," defying for a second time an ultimatum set by neighboring African countries and backed by Western diplomats.

The delay raises the possibility that the M23 rebels don't intend to leave the city they seized last week, giving credence to a United Nations Group of Experts report which argues that neighboring Rwanda is using the rebels as a proxy to annex territory in mineral-rich eastern Congo.

"We will be out of Goma on Sunday, and will go back to our initial positions in Kibumba," M23 rebel spokesman Lt. Col. Vianney Kazarama said on Friday, referring to a town 25 kilometers (15 miles) north of Goma.

The regional bloc representing the nations bordering Congo had issued a Friday deadline for the M23 fighters to retreat, after the rebels had thumbed their nose at an earlier ultimatum. Kazarama's announcement suggests the rebels are dragging their feet.

In a sign of how confused the situation remained on Friday morning, a barge carrying around 280 Congolese policemen arrived at Goma port, on the banks of Lake Kivu. The policemen had fled when the rebels took the city, and were returning to resume control of the city on Friday, as had been earlier agreed.

The Congo government police appeared disoriented, unsure what to do and they did not disembark from the barge, as M23 fighters patrolled the port.

The M23 rebels are widely believed to be supported by Rwanda, which according to the U.N. report, has provided them with battalions of soldiers, arms and financing. Congo, an enormous, sprawling Central African nation, has twice been at war with its much smaller but more affluent and better organized neighbor.

The eight-month-old M23 rebellion is led by fighters from a now-defunct rebel group, who agreed to lay down their arms on March 23, 2009, in return for being allowed to join the ranks of the Congolese army. M23 takes its name from the date of that accord, and the rebellion began in April, when hundreds of soldiers defected from the military, saying that they were not well paid and were marginalized within the army.

But most analysts believe the origin of the rebellion is a fight over Congo's vast mineral wealth, a good chunk of which is found in the North Kivu province where Goma is the capital. Starting in April, the fighters seized a series of small towns and villages in North Kivu, culminating with the capture on Nov. 20 of Goma, a population hub of 1 million and a key, mineral trading post.

Months before taking Goma, the rebels steadily made their way down the road from Kibumba, and in the weeks just before the fall of the regional capital, that artery was swarming with rebel soldiers and punctuated by checkpoints. By contrast on Friday, that same road was remarkably empty, showing no signs of rebels retreating, as they had earlier promised when they agreed to the ultimatum issued the regional African bloc, the African Union and which is supported by United States Secretary of State Hillary Clinton and other western diplomats.

Although discreet, the M23 presence in Goma was still noticeable Friday. Political officers of the movement were going about their business Friday morning, giving no sign of packing up to leave the city.

"We are leaving Goma to give a chance to peace and to make (Congolese President Joseph) Kabila assume his responsibilities," assured Stanislas Baleke, an M23 political cadre.

Although several U.N. reports have clearly indicated Rwanda's role in propping up the rebels, the U.S. and others have so far not publicly called out Rwanda, with U.S. Secretary of State Clinton sidestepping a question on the issue at a press conference this week.

But on Friday the British government announced that it will not release its next payment of budget support to Rwanda. United Kingdom International Development Secretary Justine Greening said that the >21 million ($33.7 million) of general budget support, which was due in December, is not being disbursed as a result of Rwanda's role in the conflict in Congo.

"The government has already set out its concerns over credible and compelling reports of Rwandan involvement with M23 in DRC. This evidence constitutes a breach of (our) partnership principles," he said, "And as a result I have decided not to release the next payment of budget support to Rwanda."