South Sudan's Vice President Riek Machar and his wife Angelina Teny, who serves as defence minister, have tested positive for the coronavirus, his office said on Monday.
It said that "a number of his office staff and bodyguards" had also tested positive for Covid-19.
Mr Machar said on state television that he would be in self-isolation for 14 days in his residence.
South Sudan, which is emerging from a devastating six-year civil war, has recorded 347 cases of Covid-19 and six deaths, according to the latest figures from the health ministry, also released on Monday.
Although the number is relatively low, only 3,908 tests have been conducted.
Aid agencies have been sounding the alarm over a sharp rise in cases in recent days.
Last week, officials announced the virus had reached a camp of about 30,000 displaced people who have been seeking United Nations protection in the capital Juba since 2013. Two cases have been confirmed there.
"We are particularly concerned that there have been a couple of cases that tested positive in the camp here just outside Juba. There are tens of thousands of internally displaced persons living there, so they live in quite cramped conditions," James Reynolds, from the International Committee of the Red Cross in South Sudan, said.
He said measures such as social distancing and regular hand washing would not be easily applicable in the camp.
A case has also been confirmed in a similar camp in northern Bentiu, home to about 120,000 people.
The country continues to be gripped by humanitarian emergency and hunger, even after Mr Machar and President Salva Kiir – the main rivals in the civil war – formed a unity government in February.