Sporadic gunfire and explosions have been reported as M23 rebels advance towards a key city in eastern Democratic Republic of Congo, in an offensive that has forced thousands to flee across the border into Burundi.

Residents and military sources said soldiers were fleeing the assault on Uvira, the last government-held city in the mineral-rich region.

US President Donald Trump brokered a peace deal last week between DR Congo's President Félix Tshisekedi and Rwanda's Paul Kagame to end the long-running conflict but fighting has continued.

Shops and schools have closed, with terrified residents staying indoors amid fears that rebels had taken control of some government buildings.

But South Kivu Governor Jean-Jacques Purusi dismissed reports that the rebels were in the city as "completely unfounded rumours".

Residents told the BBC that Uvira was in lockdown on Wednesday, with some reporting gunfire in the city that is just 27 km (17 miles) from Burundi's capital, Bujumbura.

A local rights official told AP news agency that there was a "risk of a massacre" if the remaining soldiers mounted strong resistance.

"It's chaotic, nobody's in charge. Uvira is done for," a Burundian officer told AFP news agency.

"Three bombs have just exploded in the hills. It's every man for himself," a resident told AFP, while another added: "We are all under the beds in Uvira - that's the reality."

Military and security sources said the rebel fighters advanced from the north, near the Burundian border.

In an interview with UN-backed Radio Okapi, Purusi denied Uvira had fallen to the M23, saying the city remained under the control of government forces.

The US, European Union, and eight European nations have accused Rwanda of supporting the rebel offensive, and have called for an immediate halt to the fighting

In a joint statement, they voiced "profound concern" about the violence, and said it had a "destabilising potential for the whole region".

They urged the Rwanda Defence Force (RDF) to "immediately halt offensive operations" in eastern DR Congo, and called on its troops to withdraw from the region.

A spokesman for the US state department said that Rwanda "continues to provide support to M23 [and] must prevent further escalation".

But Rwanda has denied any involvement in the fighting, accusing DR Congo's government and its ally, Burundi, of violating a ceasefire.

In a statement on X, the Rwandan foreign ministry said the ceasefire violation "cannot be placed on Rwanda" and said the Congolese and Burundian armies had "systematically" bombed villages close to Rwanda's border.

UN experts say Rwanda's army is in "de facto control of M23 operations".

About 200,000 people have fled their homes in eastern DR Congo since the latest round of fighting started early this month, the UN says.

It said at least 74 people had been killed, mostly civilians, and 83 admitted to hospital with wounds.

A Burundian administrative source told AFP that he had recorded more than 8,000 daily arrivals over the past two days, and 30,000 arrivals in one week.

The latest offensive comes nearly a year after the M23 rebels seized control of Goma and Bukavu, the other two main cities in eastern DR Congo.

The M23 is not part of the US-brokered peace deal, and is in separate talks with DR Congo's government in mediation efforts led by Qatar.

In a national address on Monday, Tshisekedi accused Rwanda of "deliberate violations" of the peace accord.

"This is a proxy war aimed at challenging our sovereignty over a highly strategic area, rich in critical minerals and economic potential that is crucial to the future of our nation," Tshisekedi said.

For its part, Rwanda accused the armies of DR Congo and Burundi of bombing villages near its border, forcing more than 1,000 civilians to flee into its territory.

Eastern DR Congo has been wracked by conflict for more than 30 years, since the 1994 Rwandan genocide. Several peace deals going back to the 1990s have collapsed.

Numerous armed groups have competed with the central authorities for power and control of the potential fortune in this vast nation.