International sanctions against Rwanda will reduce the incentive for Kinshasa to engage in peace talks with M23 rebels who have made lightning advances in eastern Congo this year, a proscribed Rwandan minister has said.

"As they push for sanctions against Rwanda, (Congo's president), seeing that Rwanda is being targeted, will refuse to participate in any negotiations," James Kabarebe, a Rwandan state minister for foreign affairs, said in a speech on Tuesday.

Rwanda-backed M23 rebels have seized eastern Congo's two largest cities over the past month in a conflict that has displaced around half a million people since January.

Last Thursday, the United States Treasury imposed sanctions on Kabarebe for his alleged role as a government liaison to the M23. He didn't specifically refer to the sanctions against himself in his comments.

Britain said on Tuesday it would pause some bilateral aid to Rwanda and impose other diplomatic sanctions on Kigali until there was significant progress in ending hostilities and a withdrawal of all Rwandan troops from Congolese territory, estimated by the United Nations to number several thousand.

The European Union said on Monday it would review its agreement with Rwanda for strategic minerals over Kigali's links with the rebels.

Rwanda denies providing arms and troops to M23, and says its forces are acting in self defence against the Congolese army and militias hostile to Kigali.

In his speech, Kabarebe also accused Congo's President Felix Tshisekedi, who has refused to negotiate with M23, of offering the international community minerals in exchange for sanctions.

Congo's presidential spokesperson Tina Salama did not immediately respond to Reuters' request for comment, but previously said that Tshisekedi has invited US companies to purchase strategic raw materials directly from Kinshasa, rather than materials "smuggled" through Rwanda.

African leaders on Monday appointed the former Presidents of Kenya and Nigeria and the ex-Prime Minister of Ethiopia to mediate the ongoing peace process.

A close ally of President Paul Kagame for decades, Kabarebe has played a central part in a string of Rwanda-backed insurgencies in Congo since the mid 1990s.

The region is already reeling from a humanitarian crisis, and the latest conflict has fanned fears of a regional war like those that killed millions between 1996 and 2003, most from hunger and disease.

Eastern and Southern African countries are looking into the possibility of deploying African Union (AU) troops to secure areas controlled by M23, alongside a beefed up UN peacekeeping mission.