KIGALI, Rwanda — Secretary of State Antony J. Blinken said on Thursday that he had urged the leaders of Rwanda and the Democratic Republic of Congo to end their support for militias in eastern Congo, warning that continuing to back the groups threatened stability across the Great Lakes region of Africa.
“Whoever it’s by, whoever it’s to, that support has to cease,” Mr. Blinken said at a news conference in Kigali, the capital of Rwanda. “It’s a matter of principle that applies equally. It’s not a matter of weighing one group against another.”
American and Rwandan officials estimate that more than 130 armed groups are operating in eastern Congo, which has become a battleground for militias who have maimed and murdered while profiting from the billions of dollars of minerals smuggled out of the resource-rich region. Many of the groups get weapons and financial support from the Congolese government or from other African nations.
Since late last year, hundreds of people have been killed in the area, and more than 160,000 have been displaced.
Mr. Blinken added that both Congo and Rwanda had to adhere to the fundamental principle that governments should refrain from arming nongovernmental groups. “To the extent that happens, that’s likely to perpetuate conflict and violence, not end it,” Mr. Blinken said.
In the case of Rwanda, Mr. Blinken said, there were “credible reports” that the government was supporting the March 23 Movement, known as M23, and had deployed official military forces in eastern Congo.
Mr. Blinken said that he conveyed his concerns in a meeting on Thursday with President Paul Kagame of Rwanda, a former military officer who is widely credited with rebuilding the country after a genocide in 1994. Mr. Blinken said that he had delivered the same message in a meeting with President Félix Tshisekedi of Congo in that country’s capital, Kinshasa, on Tuesday.
Mr. Blinken added that he had urged all parties to work with a mediation process on conflict in eastern Congo that is being led by Kenya and Angola.
Rwanda’s leaders say that their actions are aimed at defanging the Democratic Forces for the Liberation of Rwanda, or F.D.L.R., a militia largely made up of ethnic Hutu fighters from Rwanda and elsewhere, including ones who carried out genocide against ethnic Tutsis in Rwanda in 1994.
“Rwanda is not the cause of longstanding instability in eastern D.R.C.,” Vincent Biruta, the Rwandan foreign minister, said at the news conference with Mr. Blinken, referring to Congo. Mr. Biruta added that the F.D.L.R. was carrying out “terrorist” violence in Rwandan territory, and that his government was intent on “protecting our people.”
All parties need to “deal with the root causes of the problem” in eastern Congo, Mr. Biruta said.
At noon, after the news conference, Mr. Blinken visited a hillside memorial to the up to one million Rwandans killed in the genocide. The remains of about 250,000 Rwandans are interred beneath slabs of concrete at the site in Kigali. Mr. Blinken stood in remembrance by a wreath of yellow flowers next to the graves outdoors, then walked through dimly lit rooms that housed displays of photographs of the victims and their belongings, including clothing.
The daylong stop in Rwanda was the final leg of a three-country tour of Africa by Mr. Blinken, who also visited South Africa and Congo this week. The Africa trip followed stops in Cambodia and the Philippines. In Kinshasa, Mr. Blinken spoke to leaders there about eastern Congo, mining practices, trade, and environmental conservation and climate change. He also heard requests from Mr. Tshisekedi and other officials for him to pressure Mr. Kagame to end support to the M23 militia.
Hostility toward Rwandan leaders is widespread among Congolese citizens, and political cartoons and social media commentary in the country ahead of Mr. Blinken’s visit portrayed the United States as backing a belligerent government in Kigali.
At news conferences in Kinshasa and in Kigali, Mr. Blinken framed foreign support for militias in eastern Congo as a potential violation of territorial integrity and sovereignty, which the Biden administration has emphasized as important international principles since Russia’s invasion of Ukraine in February.
“Let me simply add that all countries have to respect their neighbors’ territorial integrity,” Mr. Blinken said in Kinshasa. “This is a proposition that we take very seriously around the world.”
“Any entry of foreign forces into the D.R.C. must be done transparently, with the consent of the D.R.C., deconflicted from the U.N. mission, and prenotified to the Security Council, consistent with the U.N. resolution,” he added, referring to the long-running and troubled United Nations peacekeeping mission in eastern Congo.
On July 31, United Nations peacekeepers in Congo opened fire at a border crossing with Uganda, killing two people and injuring at least 15 others. The deaths were part of a series of violent episodes involving peacekeepers that convulsed eastern Congo this summer. Just days earlier, at least 19 people, including three U.N. peacekeepers, were killed and 60 others injured during protests against the peacekeeping mission in the cities of Butembo and Goma.
The peacekeeping mission has been in Congo since 2010. It has nearly 13,000 people in the country, with troops and military members drawn from at least 10 countries.
At the news conference in Kigali, Mr. Blinken also said that he had raised human rights concerns with Mr. Kagame, including the case of Paul Rusesabagina, a political figure and U.S. citizen who was convicted by a court in Rwanda last September on terrorism charges.
In 1994, as the manager of a luxury hotel in Kigali, Mr. Rusesabagina gave shelter to 1,268 people during the genocide, actions that inspired an Oscar-nominated movie, “Hotel Rwanda.”
Prosecutors accused him of involvement with a militia, the National Liberation Front, that is the armed wing of a political group with which Mr. Rusesabagina, 68, is linked.
Mr. Rusesabagina disappeared on a visit to Dubai last year, then resurfaced as a prisoner in Rwanda.
Mr. Biruta, the foreign minister, gave no indication that Rwanda would free Mr. Rusesabagina, who is serving a 25-year sentence. “When we deal with people who commit crimes against our country, our people, we abide by the laws, both national and international,” he said.
Anaïse Kanimba, a daughter of Mr. Rusesabagina, said that her father was ailing and needed to be freed, and that the relationship of the United States with Rwanda “is strong enough to push for the release of our father on humanitarian grounds.”
In May, the U.S. State Department determined that Mr. Rusesabagina had been “wrongfully detained.” Last September, after his conviction, the department said that “the reported lack of fair trial guarantees calls into question the fairness of the verdict.”