Lagos, Nigeria (CNN) -- Nigerian authorities arrested 10 people believed to be gay men under a bill signed this week that bans same-sex marriages, a human rights group said.
Police detained men in various states and have dozens of pending arrests based on perceived sexual orientation, according to Amnesty International.
"Those arrested under this draconian new legislation must be released immediately and the charges against them dropped. Locking someone up for their sexual orientation violates the most basic human rights standards," Makmid Kamara, a researcher for the rights group, said in a statement Wednesday.
Nigerian police spokesman Frank Mba angrily suggested no one had been arrested due to the new law.
"I challenge Amnesty International to publish details of persons alleged to have been arrested in connection with the new anti-gay law, stating clearly when they were arrested, where they were arrested, the police station or department that carried out the arrest, etc.," Mba told CNN Thursday.
"The new anti-gay law is primarily designed to prevent same sex marriages and unions in Nigeria. So far, (to the best of our knowledge) no Nigerian has come out to declare his intention of engaging in such an illicit union. Therefore, the question that naturally arises is: how can the police arrest 'suspects or offenders' not known to them or to the law?"
In Bauchi state, Amnesty said an assistant commissioner of police confirmed that authorities had placed "a list of suspected gay people" under surveillance. The group said police arrested the men in Anambra, Enugu, Imo and Oyo states.
"Reports that the police in one state are apparently drawing up lists of members of the lesbian, gay, bisexual, transgender and intersex community to target are extremely worrying," Kamara added.
Mba took issue with that claim as well.
"Who is this assistant commissioner of police? Amnesty International should provide his name and designation. Without providing details of the sources of their stories, third parties like CNN cannot independently verify the authenticity or accuracy of such stories. The anonymity of the story raises a big credibility question.
"Bauchi State Police Command alone has a total of seven assistant commissioners of police. There are hundreds of ACPs nationwide. Thus, without properly identifying the ACP in question, I will treat the story as mere fiction."
President Goodluck Jonathan signed the bill Monday after parliament passed it last year, despite international pressure against it.
It bans same-sex marriages and civil unions, and includes sentences of up to 14 years in prison for gay couples. The bill also forbids the operation of gay clubs, societies or meetings in Nigeria. The punishment for such acts is 10 years in prison.
U.S. Secretary of State John Kerry joined the United Nations in condemning the bill.
"This law dangerously restricts freedom of assembly, association and expression for all Nigerians," Kerry said. "People everywhere deserve to live in freedom and equality. No one should face violence or discrimination for who they are or who they love."
U.N. chief Ban Ki-moon expressed concerns, saying he was alarmed by reports of arrests and torture. He said he fears the bill will lead to violence and discrimination. .
Last month, the Ugandan parliament passed controversial legislation that would make some gay acts punishable by life in prison. President Yoweri Museveni has not signed it yet.
Homosexuality is illegal in most African nations based on remnants of sodomy laws introduced during the British colonial era. The laws are perpetuated by cultural and religious beliefs.
Punishments across the continent range from fines to years in prison.
Last year, a Pew Research Center report found African and Muslim nations are the least accepting of homosexuality.
Of the 39 countries surveyed, Nigeria was the most intolerant. At least 98% of respondents in the nation said homosexuality is unacceptable.
CNN's Vladimir Duthiers reported from Lagos, and Faith Karimi from Atlanta. CNN's Nana Karikari-apau contributed to this report.