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
Team Sky's Chris Froome is set to win the 2016 Tour de France with an overall lead of four minutes 11 seconds after stage 20 to Morzine
The attempted kidnap of an RAF serviceman took place near RAF Marham, in Norfolk, on Wednesday.
Footballer Marc Crosas faces an investigation after pictures emerged of him appearing to have speared an endangered baby shark