A Congolese regional governor has told the BBC that rebels will not take the main eastern city of Goma, following fierce fighting.
Julien Paluku said that the rebels had telephoned him to say they would be “spending the night” in Goma.
Mr Paluku said 150 rebels had been killed but the rebels disputed these figures, saying no-one had died.
The fighting is the most serious since July in the mostly lawless but resource-rich eastern DR Congo.
Nearly 500,000 people have fled their homes since April when the rebels mutinied from the army.
The fighting has been taking place around the village of Kibumba about 30km (19 miles) north of Goma in North Kivu province.
A body count showed that more than 150 rebels and two government soldiers had been killed, said Mr Paluku, the North Kivu governor.
Thousands of people have fled the latest fighting, which lasted until Friday morning, he said.
Mr Paluku told BBC Afrique he had received a phone call from M23 military spokesman Lt Col Vianney Kazarama who told him that the rebels would “spend the night” in Goma, a city of some 400,000 people.
However, government forces would repel any attack on the city, Mr Paluku said.
On Thursday, the army spokesman in Goma, Olivier Hamuli, said 44 rebels had been killed – and one high-ranking officer from the army also died.
Lt Col Kazarama told the BBC that no rebels had been killed but two had been injured.
The UN mission in DR Congo, Monusco, said it could not confirm any casualty figures.
The BBC’s Gabriel Gatehouse witnessed the Congolese army using tanks and helicopters against the rebels on Thursday.
Both sides accuse the other of starting the conflict.
Government spokesman Lambert Mende said “51 bodies [of rebels] wearing Rwandan army uniforms have been collected” from the battlefield, AFP reports.
On Tuesday, Uganda closed the Bunagana border crossing near Goma.
This followed a request from the DR Congo government, which said the M23 was illegally raising money from people travelling between the two countries to finance its operations.
Last month, a UN panel of experts said Rwanda and Uganda were supplying M23, also known as the Congolese Revolutionary Army, with weapons in what is seen as an on-going battle for control of the region, which is rich in minerals.
Rwanda and Uganda strongly deny the allegation – Rwanda has called on both sides to stop fighting, saying stray bullets have fallen on its side of the border, injuring civilians.
The UN and US imposed a travel ban and asset freeze earlier this week on the group’s leader, Sultani Makenga.
The UN has a large force in DR Congo to help the government establish its authority in the mostly lawless east.