The M23 rebel group said on Wednesday that two of its commanders had been killed in fighting with army troops in eastern Democratic Republic of Congo (DRC).
The two men died in a drone strike by the Congolese army on Tuesday in the town of Kitshanga in North Kivu province's Masisi territory, according to security sources speaking on condition of anonymity.
After years of dormancy, the M23 (March 23 Movement) rebels took up arms again in late 2021 and have seized vast swathes of the province.
Neighbouring Rwanda has been accused by Western governments and the United Nations of supporting the M23, though Kigali denies the claim.
The fighting has pitted the M23 rebels against the Congolese army, armed militias known locally as "wazalendo" and two private military companies contracted by the government.
Last month, the army and its allies began using Chinese-made combat drones against rebel positions.
"The Kinshasa regime violated yet again the imposed ceasefire by attacking our forces on the front lines and carrying out acts of assassination behind our front lines, killing two of our commanders," the M23 said in a statement, adding it would "respond accordingly".
It did not give the commanders' names.
Sources within the M23 said they were the rebel group's intelligence chief "colonel" Mberabagabo, alias "Castro", and strategy adviser Eraston Bahati.
Violent clashes took place on Tuesday in several parts of Masisi, local sources said.
The fighting appeared to have calmed down Wednesday, apart from around Nyiragongo, just north of the provincial capital Goma where residents spoke of detonations and army fighter planes.
Troops from the 10-nation Southern African Development Community (SADC) have been discreetly arriving in the DRC since the middle of December.
A senior army officer said on Tuesday the Kinshasa was counting on them to help it regain ground from the M23 militia.
The troops will take over from an East African peacekeeping force, whose mandate was ended by Kinshasa which accused it of colluding with the rebels instead of fighting them.
Also on Tuesday, Rwanda said it shot and killed a Congolese soldier and arrested two others after they crossed the border and opened fire.
The DRC military said the soldiers were on patrol and found themselves on Rwandan territory "by mistake".