Ugandan President Yoweri Museveni has put a bill imposing strict penalties for homosexuality on hold to give scientists a chance to prove that homosexuality could be triggered by genes and is not a "lifestyle choice".
Homosexuality is taboo in many African countries and illegal in 37. Few Africans are openly gay, as they fear imprisonment, violence and loss of their jobs.
The US warned that signing the bill into law would complicate its relationship with Uganda, a regional ally in the fight against al-Shabab in Somalia, to whom it gives more than $400m in aid every year.
Museveni dismissed the US threat, but said in a statement dated February 18 and seen by the Reuters news agency on Friday that he would not sign the proposed law until after hearing from scientists.
"What I want them to clarify is whether a combination of genes can cause anybody to be a homosexual," Museveni said in the statement. "Then my task will be finished and I will sign the bill."
Museveni said local scientists would carry out the study but he invited US scientists to help. It was unclear how long the inquiry would last.
Tamale Mirundi, presidential spokesman, told Reuters on Friday the bill would be on hold for now "until more conclusive research is done, and that's what the president is saying in that letter".
The bill, which was introduced in 2009, initially proposed a death sentence for homosexual acts, but was amended to prescribe jail terms including life in jail for what it called aggravated homosexuality.
That category includes gay sex with a minor, where the victim is infected with HIV and where the victim is vulnerable, such as a disabled person.
Museveni last month said he would shelve the bill, which has drawn fire from Western donors and human rights groups.
But on February 14, he told legislators from his ruling National Resistance Movement party that he planned to sign the law after receiving an opinion from a group of Ugandan scientists that homosexuality was a lifestyle choice that had no connection to genes.
The president is trying to please a conservative local constituency vehemently opposed to homosexuality while at the same time avoiding alienating Western aid donors.
Museveni may have been under pressure to sign the bill after his party backed him as the flag bearer in the 2016 presidential elections, analysts said.
"He could not deny the wish of the MPs who had just given him what he wanted," political analyst Peter Mwesige, who heads the Africa Centre for Media Excellence, said.