In a statement by Desmond and Leah Tutu, the pair said they were "disheartened" by Ugandan President Yoweri Museveni's decision to sign an anti-gay bill.
The statement reads: "When President Museveni and I spoke last month, he gave his word that he would not let the Anti-Homosexuality Bill become law in Uganda. I was therefore very disheartened to hear last week that President Museveni was re-considering his position...
"We must be entirely clear about this: The history of people is littered with attempts to legislate against love or marriage across class, caste and race. But there is no scientific basis or genetic rationale for love. There is only the grace of God.
The statement added: "There is no scientific justification for prejudice and discrimination, ever. And nor is there any moral justification. Nazi Germany and apartheid South Africa, among others, attest to these facts."
More top news
Hundreds of people are feared to have drowned after a boat packed with migrants sank off the coast of Libya, trapping many in the hold.
Thousands are missing out on the best cancer treatments, research has found, with 50% unaware of more advanced types of radiotherapy.
Weather experts say most of the country should brace itself for showers, with thunderstorms and some heavy rain in parts.