South African President Cyril Ramaphosa is receiving treatment for "mild COVID-19 symptoms" after testing positive for the virus on Sunday, his office said in a statement.

Ramaphosa, 69, began feeling unwell earlier Sunday after leaving a state memorial service in Cape Town in honor of Frederik Willem de Klerk, South Africa's last apartheid president and a Nobel laureate, who died last month. Ramaphosa, who is fully vaccinated against COVID-19, was experiencing "mild" symptoms and a test confirmed he was infected, according to his office. The statement didn't say whether he has the omicron variant, which was discovered by scientists in southern Africa last month and is spreading rapidly.

Ramaphosa is self-isolating in Cape Town and is being monitored by the South African Military Health Service. He has delegated all his responsibilities to Deputy President David Mabuza for the next week, his office said.

Last week, Ramaphosa traveled with a delegation to four West African nations. He and the members of the South African delegation were all tested for COVID-19 in each of the countries during their trip. They returned to South Africa on Dec. 8, after testing negative in Senegal. Ramaphosa tested negative again upon arriving in Johannesburg that day, according to his office.

The statement advised people who had contact with the South African president on Sunday to watch for symptoms or to get tested for COVID-19.

"President Ramaphosa says his own infection serves as a caution to all people in the country to be vaccinated and remain vigilant against exposure," his office said in the statement. "Vaccination remains the best protection against severe illness and hospitalization."

-ABC News' Christine Theodorou

The number of people who have died from COVID-19 in the United States surpassed 800,000 on Tuesday, according to real-time data compiled by Johns Hopkins University's Center for Systems Science and Engineering.

The figure is greater than the approximately 700,000 Americans who have died from AIDS-related illnesses over the last four decades, and it's higher than the total number of U.S. troops who have fallen in battle since 1900.

Since last December, when the first COVID-19 vaccines were being administered, an additional 500,000 people in the U.S. have died from the virus.

Of those, some 230,000 have died since April 2021, when U.S. President Joe Biden announced COVID-19 vaccines were widely available to every American over the age of 18.

-ABC News' Arielle Mitropoulos