Uganda’s President Yoweri Museveni has asked the US to advise a team of scientists about homosexuality, as he considers whether to sign a law increasing punishments.
Mr Museveni’s spokesman said the president would not sign the law until he had received the scientific advice.
Last week he said he had decided to sign the Anti-Homosexuality Bill, which parliament has passed.
The US has warned that enacting the bill would complicate relations.
President Barack Obama described it as an affront, and a danger to, Uganda’s gay community.
The US is one of Uganda’s largest foreign aid donors.
Homosexual acts are already illegal in Uganda. Under the proposed legislation, those convicted of homosexual acts could face life imprisonment.
The law would also make it a crime not to report gay people.
In a statement, Mr Museveni said: “I… encourage the US government to help us by working with our scientists to study whether, indeed, there are people who are born homosexual.
“When that is proved, we can review this legislation.”
He originally refused to sign the bill, saying that it was wrong to punish people who were born “abnormal”.
But then a team of Ugandan scientists advised him that homosexuality was a behavioural choice and so should be punished.
The private member’s bill originally proposed the death penalty for some offences, such as if a minor was involved or the perpetrator was HIV-positive, but that clause has been dropped.
Uganda already has legislation banning gay sex between men, but the proposed law sharply tightens restrictions – and covers lesbians for the first time.
Promotion of homosexuality – even talking about it without condemning it – would also be punishable by a prison sentence.