US Secretary of State Antony Blinken has said that Washington is very concerned about what he called credible reports that Rwanda has provided support to rebels in the neighbouring Democratic Republic of Congo.
Mr Blinken, speaking in the Congolese capital, Kinshasa, called on all parties to halt any co-operation with the M23 rebel group.
The conflict in eastern DR Congo was a key focus during his meeting with President Felix Tshisekedi on Tuesday.
M23 controls a large swathe of territory in the region, and its attacks have displaced tens of thousands of people.
Mr Blinken is heading for Rwanda on the next stage of his Africa tour.