KAMPALA, Uganda — South Sudan, which gained independence from Sudan last year after decades of civil war, has expelled a United Nations human rights officer after the government objected to a report raising allegations of atrocities by South Sudan’s army.

Hilde F. Johnson, the head of the United Nations Mission in South Sudan, described the expulsion as a “breach of the legal obligations” of South Sudan’s government “under the charter of the United Nations.”

Human rights monitoring “must be protected,” Ms. Johnson said in a statement on Sunday. “Human rights violations and discrimination were at the core of the South Sudanese struggle during decades of civil war.”

The report, published by the United Nations in June, said South Sudan’s military had committed widespread abuses while trying to disarm civilians in Jonglei State after a surge of ethnic violence. South Sudan condemned the report as one-sided.