KINSHASA, Democratic Republic of Congo — The United Nations high commissioner for human rights blamed the government of the Democratic Republic of Congo on Thursday for using excessive force during political demonstrations and riots this week that might have killed more than 50 people.

The unrest convulsed Kinshasa, the capital, as the country slides into a period of dangerous political uncertainty. The president, Joseph Kabila, is required by the Constitution to step down in December, but he has shown no inclination to do so, and his government has not announced when the next election might be.

For the first time in days, most stores reopened Thursday and a beat of normal life returned to Kinshasa. The streets were plugged with traffic, and moving markets of thousands of women selling produce and baguettes from atop their heads streamed by.

On Monday, opposition supporters rampaged through several Kinshasa slums burning cars, looting banks and attacking police officers and the offices of Mr. Kabila’s political party.