The Democratic Republic of Congo and the Rwanda-backed militia M23 released a joint statement late on Wednesday announcing a commitment to end the conflict that has raged along the border of the two countries since January, killing thousands.

The announcement came as a surprise to some observers. Felix Tshisekedi, the president of Congo, had long said his country would not negotiate directly with M23, which has lately occupied large swaths of Congolese territory, seizing cities and mines rich with critical minerals.

In the joint statement, the two sides said they shared a “commitment to an immediate cessation of hostilities,” and that they would work toward a lasting peace agreement.

Fred Bauma, the executive director of the Congolese research institute Ebuteli, called the joint statement “unprecedented,” given that Mr. Tshisekedi has said repeatedly that his country would only negotiate directly with Rwanda.

The United States and the United Nations have accused Rwanda of financing and directing M23, an accusation that Rwanda denies.

The announcement on Wednesday was a rare bright spot in a conflict that has roots going back three decades. In the mid-1990s, as a genocide gripped Rwanda, millions of people crossed into neighboring Congo, leading to two wars that together killed around six million people, according to U.N. experts. Since January, those hostilities have escalated again.