"It seems that the advances have stopped," UN peacekeeping chief Herve Ladsous told reporters on Tuesday.
"If anything there were signs tonight that they were either getting out of Goma or getting ready to do that."
Ladsous said the withdrawal could only be confirmed by the UN peacekeeping mission in DR Congo on Wednesday.
M23 rebels took over Goma on Tuesday last week as they made a lightning advance through the mineral-rich North Kivu province. The rebels have agreed to withdraw to positions 20km north of Goma under a deal struck in Kampala on Monday with an East African regional group.
Ladsous said the UN's main military advisor, General Babacar Gaye, would head for the DRC and other East African countries on Tuesday to work out details of the withdrawal deal.
He said this would include the working of a proposed neutral zone, which controls Goma airport and is currently in the hands of the UN mission Monusco, and how to set up a proposed international neutral force for DRC.
M23's military leader Sultani Makenga announced earlier that the rebels had agreed to leave by Thursday. But there was confusion as they set conditions that have been rejected by DRC.
The rebellion erupted in April when the M23, which UN experts have said is backed by neighbouring Rwanda, broke away from the DR Congo army, complaining that a 2009 deal to end a previous conflict had not been fully implemented. – AFP