Olumide Makanjuola, an executive director of the Initiative For Equality in Lagos, speaks to the press in Nigeria on Wednesday. Sunday Alamba/AP

A "witch hunt" for gay people has led to 10 detentions in at least four of Nigeria's 36 states, Amnesty International said Wednesday, blaming a new law criminalizing gay organizations and meetings as well as same-sex marriage.

Nigerian human rights defenders say they fear further persecution of gay people under the law in a notoriously corrupt country where police are known to make arrests to extort money and blackmail victims.

"With the stroke of a pen, President (Goodluck) Jonathan has essentially turned Nigeria into one of the world's least tolerant societies," Amnesty International said in a statement calling for the law to be withdrawn without delay.

"Amnesty International is calling on the authorities to stop all further arrests and put an immediate end to this witch hunt," the organization said.

Since Christmas, 38 people have been arrested in the northern state of Bauchi and some have been charged in court with belonging to a gay organization. Amnesty said another 10 people have been detained since Monday in four southern states.

It said police in Bauchi have also confirmed they have a list of suspects of minority sexual orientation who are under surveillance that also is being used to "find out who their victims are."

Jonathan signed the law despite international condemnation. Secretary-General Ban Ki-moon expressed deep concern on Wednesday at the new law, which, according to his press office, he fears could "fuel prejudice and violence."

The European Union and rights groups have joined in condemning the new law, which they say could endanger programs to fight HIV-AIDS.

EU foreign policy chief Catherine Ashton said the act appears to contradict fundamental rights of all Nigerians, including freedom of association, conscience and speech.

Nigeria already had a law making sodomy illegal, and gay people can get lynched and beaten to death or legally executed by stoning for the offense under sharia law, which prevails in nine of the 36 states.

That has led some critics to suggest the issue is being used for political reasons in a country deeply divided on religious and tribal grounds. Nigeria's more than 160 million people are almost equally divided between the predominantly Muslim north and mainly Christian south, but many Christians and Muslims in Nigeria are united in the condemnation of homosexuality.

Nigerian media remained largely silent on the issue.

The bill bans all gay associations, with penalties of up to 14 years' imprisonment for marriage.

Al Jazeera and wire services