Streets were empty, shops shuttered and soldiers fled the eastern DR Congo city of Uvira on Wednesday, a day after M23 rebels entered the strategic city's outskirts, prompting Burundi to close its border.

M23's assault comes less than a year after the rebel group seized control of Goma and Bukavu, two key provincial capitals in the mineral-rich eastern Democratic Republic of Congo, which has been plagued by conflict for three decades.

Its latest rapid advance – launched on December 1 in South Kivu province against a Congolese army backed by Burundian forces – also comes just days after the signing of an agreement aimed at ending the conflict brokered by US President Donald Trump.

Burundi, which neighbours both the DRC and Rwanda, views the prospect of Uvira falling to M23 as an existential threat.

'Military zones'

Uvira sits across Lake Tanganyika from the Burundian economic capital Bujumbura, with only around 20 kilometres between the two cities.

The main border posts with the DRC were closed on Tuesday afternoon and are now considered "military zones", military and police sources told AFP.

Congolese President Felix Tshisekedi and his Rwandan counterpart Paul Kagame inked the peace deal in Washington last Thursday.

The agreement – which Trump called a "miracle" deal – includes an economic component intended to secure US supplies of critical minerals present in the region, as the United States seeks to challenge China's dominance in the sector.

City empties

However, M23 troops entered Uvira, a city of several hundred thousand residents, from the north late on Tuesday, security and military sources said.

Several Congolese army soldiers and members of pro-Kinshasa fighters were still seen in the area, military sources and witnesses said.

A few gunshots were reported.

The city nestled between mountains and Lake Tanganyika had already largely emptied on Tuesday as soldiers, police and administrative personnel fled the M23's advance.

Mass displacements

More than 30,000 Congolese have fled the fighting and arrived in Burundi in the space of a week, a Burundian local administrative official and a UN source said on Tuesday.

According to an initial estimate by the UN's humanitarian agency OCHA, more than 200,000 people have been displaced within South Kivu province since December 2, while thousands of others have crossed the border into neighbouring countries especially Burundi but also Rwanda.

Rwanda accused the DRC and Burundi of deliberately violating the peace agreement, in a statement on Wednesday.

A day earlier, the United States and European powers urged the M23 to "immediately halt" its offensive and for Rwanda to pull its troops out of the eastern DRC.

Burundian support for DRC

According to UN experts, M23 is reportedly backed by Rwandan troops, but Kigali denies the allegations.

Burundi, which has tense relations with Rwanda, deployed about 10,000 soldiers to the eastern DRC in October 2023 as part of a military cooperation agreement, and security sources say reinforcements have since taken that presence to around 18,000 men.