Two hundred thousand people have fled their homes in eastern Congo in recent days, the United Nations (UN) said, as Rwanda-backed rebels march on a strategic town just days after Donald Trump hosted the Rwandan and Congolese leaders to proclaim peace.

In a statement released late on Monday, the UN said at least 74 people had been killed, mostly civilians, and 83 admitted to hospital with wounds from escalating clashes in the area in recent days.

Local officials and residents said the Rwanda-backed M23 group has been advancing towards the lakeside town of Uvira on the border with Burundi, and battling with Congolese troops and local groups known as Wazalendo in villages north of the town.

The US president hosted the presidents of Rwanda and Congo in Washington on Thursday for a ceremony to sign a pact affirming US and Qatari-brokered commitments to end the war.

"Today we're succeeding where so many others have failed," Trump said, claiming his administration had ended a 30-year conflict that had led to the deaths of millions.

Reuters reported on Monday that the rebels had captured Luvungi, a town that had stood as the front line since February, and that fierce fighting was underway near Sange and Kiliba, villages further along the road towards Uvira from the north. 

Rwanda denies supporting the rebels in Congo, although Washington and the United Nations say evidence of Rwandan backing is clear. Prior to the latest upsurge in fighting, the conflict had already displaced at least 1.2-million people.

Reuters could not determine whether the rebels had captured Sange. A local official and several local residents said they had fled ahead of M23's expected arrival. M23 said it had captured the town. A Congolese army spokesperson did not respond to a request for comment.

The State Department said late on Monday that the US was deeply concerned by the ongoing violence.

"Rwanda, which continues to provide support to M23, must prevent further escalation," a spokesperson said.

In a speech to lawmakers on Monday, Congo's president Felix Tshisekedi accused Rwanda of violating the commitments it made in Washington.

A senior Trump administration official said Washington was monitoring the situation, working with both Congo and Rwanda, and that "the president has made clear to both sides that implementation is what he will judge, and as he stated, he is expecting immediate results."