The Rwandan government has condemned the US decision to sanction a government minister for his alleged role in the conflict in the east of neighbouring Democratic Republic of Congo.

Announcing the financial sanctions on Thursday, the US Treasury Department said Rwanda's Minister of State for Regional Integration James Kabarebe, a former army chief, was central to his country's support for the M23 rebel group.

Also sanctioned was Lawrence Kanyuka, the M23's spokesman, as well as two companies he controls in Britain and France, the US Treasury said.

On Friday, the UK said there would be "consequences" for Rwanda over its alleged role in DR Congo.

Responding to the US move, Rwanda's foreign ministry said the sanctions would not resolve the conflict in the DR Congo, terming them "unjustified and unfounded".

They come as the M23 appears to be continuing its advance after capturing two major cities in recent weeks in the mineral-rich east of DR Congo.

The rebel group, mainly comprised of ethnic Tutsis, has seized the cities of Goma and Bukavu - sparking a major humanitarian crisis that left families devastated.

Western powers have accused Rwanda of supporting the M23 with arms and as well as backing from the Rwanda Defence Force (RDF), accusations Rwanda denies.

The Treasury Department on Thursday said Kabarebe was sanctioned because "he is central to Rwanda's support" for the M23 armed group.

It said Kabarebe together with Kanyuka were "linked to violence and human rights abuses" in DR Congo.

"Today's action underscores our intent to hold accountable key officials and leaders like Kabarebe and Kanyuka, who are enabling the RDF and M23's destabilizing activities in the eastern DRC," said Bradley Smith, acting Under Secretary of the Treasury for Terrorism and Financial Intelligence.

"The United States remains committed to ensuring a peaceful resolution to this conflict."

But Rwanda dismissed the US action, saying Kigali's aim was only to secure its border and an "irreversible end to the politics of armed ethnic extremism in our region".

"Rwandans have the right to live in peace and without the perpetual threat of insecurity originating from the DRC," the ministry statement stated.

"Punitive measures, including sanctions, make no contribution toward long-term security, peace and stability for all the countries of the Great Lakes region," it added.

DR Congo welcomed the US sanctions, saying it wanted to see more such measures.

"This marks the beginning of a long series of sanctions that we want to be more robust from the UN Security Council, the European Union and other partners in order to force Rwanda to withdraw its troops and cease its criminal activities on our soil," government spokesman Patrick Muyaya said in a statement posted on social media.

Addressing G20 foreign ministers in South Africa on Friday, UK Foreign Secretary David Lammy termed the reported involvement of Rwandan troops a "blatant breach of the UN Charter which risks spiralling into a regional conflict".

Speaking at the venue Brazilian Foreign Minister Mauro Vieira condemned the recent attacks on the UN forces and regional peacekeepers in DR Congo.

On its part, China maintained that it "firmly supports the African people in independently resolving African problems and opposes external interference in the internal affairs of African countries".

Additional reporting by Jewel Kiriungi