Leading rights groups have called on Gambian President Yahya Jammeh not to approve tough new anti-gay legislation.
Homosexual acts are already illegal in The Gambia, but MPs passed a bill on 25 August imposing life sentences for "aggravated homosexuality".
The bill promoted "state-sponsored homophobia", the rights groups said.
Mr Jammeh is known for his strong opposition to gay rights. He has called gay people "vermin" and once threatened to behead them.
Uganda's Constitutional Court struck down a similar law last month on the grounds that it was passed by MPs without a quorum.
Its ruling followed an outcry from rights groups and Western governments - US President Barack Obama described the legislation as "odious".
Amnesty International and Human Rights Watch (HRW) said the definition of "aggravated homosexuality" was vague in The Gambian bill.
Among those who could be given the life sentence were "repeat offenders" and people living with HIV who are suspected to be gay or lesbians, they said in a joint statement.
A person who had homosexual relations with a minor could also be convicted of "aggravated homosexuality", Reuters news agency reports.
"President Jammeh should not approve this profoundly damaging act that violates international human rights law," said Stephen Cockburn, Amnesty's deputy regional director for West and Central Africa.
Graeme Reid of HRW said it would "only heap further stigma on people who are already marginalised and living in a climate of deep fear and hate in Gambia".
Under current laws, homosexual acts are already punishable by up to 14 years in prison in The Gambia.
Mr Jammeh has 30 days from the date the bill was passed to sign it into law or return it to parliament for further review.
The Gambia is a popular tourist destination, famous for its beaches.