Using a list of names supposedly garnered through torture, Nigerian authorities have launched a manhunt for gay men.
Nigerian President Goodluck Jonathan signed a bill that criminalises same-sex relationships, the presidency said, defying pressure from Western governments to respect gay and lesbian rights.
The bill, which contains penalties of up to 14 years in prison and bans gay marriage, same-sex "amorous relationships" and membership of gay rights groups, was passed by the national assembly last May but Jonathan had delayed signing it into law.
Dorothy Aken'Ova, executive director of the country's International Centre for Reproductive Health and Sexual Rights, said that the legislation, hailed the "Jail the Gays" law, had led to mass arrests.
Police in Bauchi state, she claimed, had a list of 168 purportedly gay men, of whom 38 had been arrested.
The laws, she cautioned, will endanger medical programmes combating HIV-Aids in the gay community. Nigeria has the second-largest HIV epidemic globally with an estimated 3.4 million people living with HIV.
Responding to the spread of anti-gay legislation,Kerry said: "The United States is deeply concerned by Nigeria's enactment of the Same Sex Marriage Prohibition Act. Beyond even prohibiting same-sex marriage, this law dangerously restricts freedom of assembly, association and expression for all Nigerians.
"[The law] is inconsistent with Nigeria's international legal obligations and undermines the democratic reforms and human rights protections enshrined in its 1999 constitution," he added.
"People everywhere deserve to live in freedom and equality. No one should face violence or discrimination for who they are or who they love."