They noted that disruptions to treatment could result in hundreds of thousands of HIV-related deaths.
Byanyima pointed out that the right to health meant that no one disease should be fought at the expense of another.
It warned that a break in response could also trigger a rise in tuberculosis in sub-Saharan Africa.
“In 2018, no fewer than 470,000 people died of AIDS-related complications in Sub-Saharan Africa,” according to the organisation.
It said an estimated 25.7 million people were living with the virus, with 16.4 million on antiretroviral therapy.
“The terrible prospect of half a million more people in Africa dying of AIDS-related illnesses is like stepping back into history.
“We must read this as a wake-up call to countries to identify ways to sustain all vital health services,” the WHO chief emphasised.
Ghebreyesus noted that some countries were already taking “important steps” to maintain their health services.
He said they were doing that by allowing people to collect bulk packs of therapies and other essential commodities, including self-testing kits.
“We must also ensure that global supplies of tests and treatments continue to flow to the countries that need them,” he added.
Edited By: Angela Okisor/Muhammad Suleiman Tola (NAN)