Congo and Rwanda plan to sign an agreement in Washington on Friday to promote peace and economic development, sources told Reuters, part of a diplomatic push to end violence after an advance by Rwandan-backed rebels in eastern Congo.

The agreement, expected to be signed by the two countries' foreign ministers at a ceremony with US Secretary of State Marco Rubio, comes as Washington is in talks to invest billions of dollars in mineral-rich Congo. Rwanda said this week it was also speaking to Washington about a possible minerals deal.

Congo has seen a surge in violence after Rwandan-backed M23 rebels launched a major offensive in January that led to the capture of the two largest cities in the east.

The United Nations and Western governments say Rwanda has provided arms and troops to M23. Rwanda denies backing M23 and says its military has acted in self-defence against Congo's army and a militia founded by perpetrators of the 1994 genocide.

Both Qatar and the US have shown an interest in mediating a resolution. The Gulf state has long positioned itself as a peacemaker, while Washington is interested in accessing a greater share of Congo's mineral wealth.

A diplomatic source said the agreement to be signed on Friday aims to foster a "pathway to peace, stability, and integrated economic development" in eastern Congo and "the resumption of normal bilateral relations".

Another source briefed on the agreement said it was intended to build investor confidence.

The Trump administration has taken a special interest in Congo since a Congolese senator contacted US officials to pitch a minerals-for-security deal this year.

Washington wants greater access to minerals like copper, cobalt and lithium, which are used in mobile phones and electric cars, and are currently exploited predominantly by China and its mining companies.