ADDIS ABABA, Ethiopia — Weeks after receiving the Nobel Peace Prize, Prime Minister Abiy Ahmed is coming under harsh criticism over his silence in the face of protests this week that police said had resulted in the deaths of 67 people.

Mr. Abiy remained at a summit meeting of African leaders in the Black Sea resort town of Sochi, Russia when thousands of people took to the streets of the Ethiopian capital and several regional towns on Wednesday.

The protests were spurred by a prominent critic of the prime minister who had accused the police of plotting an attack on him. The critic, Jawar Mohammed, is the founder of an independent media network, and claimed that there was a plan to arrest or possibly kill him at his house in the capital, Addis Ababa.

The accusations stoked longstanding tensions in Ethiopia, the second-most populous nation in Africa, and drove hundreds of Mr. Jawar’s ethnic Oromo supporters to gather outside his home.