The M23 fighters have warned foreign troops backing the DR Congo army in a decades-old conflict to leave immediately

M23 rebels in eastern Democratic Republic of the Congo (DR Congo) have claimed they captured hundreds of Burundian soldiers during recent fighting near the border town of Uvira, marking a major escalation in a conflict that has continued despite a US-brokered peace deal.

Officials from the Congo River Alliance (AFC), a rebel coalition which includes the M23 movement, said the Burundian troops were seized during clashes with forces backing the Congolese Army in South Kivu province.

Burundi has deployed troops to eastern Congo for several years in support of Kinshasa's campaign against armed groups operating in the region.

"The AFC/M23 declares its readiness to hand over to the government of Burundi military personnel captured on the battlefield," the group's spokesperson, Lawrence Kanyuka, said in a statement on Monday.

READ MORE: Rebels seize key DR Congo city despite Trump peace deal

Busu Bwa Ngwi, the M23-appointed governor of South Kivu, also said on Saturday that the rebels still intend to "reclaim all provinces" and warned Burundian soldiers and other foreign forces "to return to their countries immediately."

The reported capture comes days after M23 fighters seized Uvira, a strategic city on Lake Tanganyika close to the Burundi border. The DR Congo government said more than 100 people have been killed and thousands forced to flee in the offensive, which it said was backed by Rwanda's Defense Forces.

The fighting has unfolded despite Congolese President Felix Tshisekedi and his Rwandan counterpart Paul Kagame signing an accord in Washington earlier this month, aimed at easing tensions and halting violence in eastern DR Congo. US President Donald Trump, who mediated the deal, hailed it as a "historic" end to three decades of armed conflict in the region.

Congolese officials have since accused Rwanda of breaching its commitments under the deal by failing to halt actions that undermine security in eastern Congo. Kigali has repeatedly denied involvement, insisting the escalation is the result of attacks by the Congolese army and its Burundian allies.

On Saturday, US Secretary of State Marco Rubio said Rwanda's actions in DR Congo were a "clear violation of the Washington Accords" and vowed to "take action to ensure promises made to the president are kept."