Washington on Monday reiterated fears that Rwanda is supporting a rebellion in the eastern Democratic Republic of Congo (DRC), whose rapid advances have led Kinshasa to expel the border country's ambassador.
During a visit to both countries in August, U.S. Secretary of State Antony Blinken warned of "credible" reports of Rwandan support for the "March 23 Movement" (M23), a former Tutsi rebellion.
"State support for armed groups is unacceptable and we reiterate our concerns about Rwanda's support for M23," U.S. diplomatic spokesman Ned Price told reporters.
"We encourage countries in the region to work together to restore peace, security, and respect while respecting each other's sovereignty and territorial integrity," he added.
He said U.S. officials "have been in frequent contact" with their Rwandan and DRC counterparts over the past week as tensions have risen.
After several weeks of calm, the M23 has been advancing since October 20 into Rutshuru territory, north of Goma.
The "March 23 Movement" is a former Tutsi rebellion that took up arms again at the end of 2021, blaming Kinshasa for not respecting agreements on the reintegration of its fighters.
Kinshasa announced on Saturday evening the expulsion of the Rwandan ambassador to the DRC, after months of tensions and accusations of support for the M23, denied by Kigali, which in turn claims that the DRC is collaborating with Rwandan Hutu rebels.
Relations between Rwanda and the Democratic Republic of Congo are as conflicted as they are historic, mired for nearly 30 years in the aftermath of the 1994 Rwandan genocide.