The authorities in Kinshasa on Saturday announced they were expelling the Rwandan ambassador as M23 rebels they accuse Kigali of supporting made fresh gains in the east of the troubled country.
The announcement, made by government spokesman Patrick Muyaya, came after a government meeting to assess the security situation in the Democratic Republic of Congo.
The latest advance by rebel fighters prompted the UN peacekeeping mission there to increase its "troop alert level" and boost support for the army.
Muyaya said that in recent days "a massive arrival of elements of the Rwandan element to support the M23 terrorists" against DR Congo's troops had been observed.
"This criminal and terrorist adventure" had forced thousands of people to flee their homes, he added.
Given Rwanda's continued support for the rebels, the defence council, presided over by President Felix Tshisekedi, had decided to ask the government to give Rwandan ambassador Vincent Karega 48 hours to leave the country.
M23 rebel fighters have seized control of Kiwanja and Rutshuru-centre along the strategic RN2 highway in the eastern province of North Kivu, local officials and witnesses told AFP by telephone earlier Saturday.
Rebels had also been seen at Rugari, just 30 kilometres (20 miles) down the RN2 from the provincial capital Goma, which it links with the north and Uganda.
Four peacekeepers were wounded by mortar fire and shooting at Kiwanja, the mission announced.
"Kiwanja and Rutshuru-centre are in M23 hands," said civil society representative Jacques Niyonzima.
"The rebels have held two meetings and told local people to go about their work and those displaced to return to their villages, saying security was now guaranteed," he said.
At Kiwanja, "in our area we recorded three deaths, a man, a woman and her child, killed by shells that landed on houses", said local resident Eric Muhindo.
A general hospital official in Rutshuru added: "There were several wounded in Kiwanja after a small amount of resistance".
"Calm has returned. People are moving about and shops are opening," the official said, asking not to be named.
The UN's MONUSCO mission condemned "the hostile acts of M23" and called for an immediate halt to the fighting.
The mission said on Twitter it was providing "air support, intelligence and equipment" as well as medical assistance.
The peacekeepers said they were "mobilised in support" of DRC's army after residents reported at least 10 people dead since Sunday and dozens more injured near the RN2.
MONUSCO said it had set up an "operations coordination centre" with the army and was carrying out reconnaissance and surveillance flights, but did not provide further details about the alert level.
M23, a mostly Congolese Tutsi group, resumed fighting in late 2021 after lying dormant for years, accusing the government of having failed to honour an agreement over the demobilisation of its fighters.
It has since captured swathes of territory in North Kivu, including the key town of Bunagana on the Ugandan border in June.
The front line between Congolese troops and M23 rebels had been calm in recent weeks until last week, when clashes erupted again.
Last Sunday, M23 fighters captured the village of Ntamugenga in the Rutshuru area. It lies four kilometres (less than three miles) from the RN2 where the clashes spread on Thursday.
The UN humanitarian affairs office in the DRC said this week around 34,500 people had fled the Rutshuru region.
The group's resurgence has destabilised regional relations in central Africa, with the DRC accusing its smaller neighbour Rwanda of backing the militia.
Rwanda denies the charges and counters that DRC works with a notorious Hutu rebel movement involved in the 1994 genocide of Tutsis, the Forces for the Liberation of Rwanda (FDLR), which Kinshasa also denies.
A report by independent UN experts seen by AFP in August found that Kigali had provided direct support to the M23.
And this week a US representative to the United Nations spoke of Rwandan defence forces providing assistance to the M23.
Angola's President Joao Lourenco said he would dispatch his Foreign Minister Tete Antonio to DR Congo to mediate the dispute, UN Secretary-General Antonio Guterres said following a phone call between the leaders.