Human rights activists said 14 young boys have been assaulted with wooden clubs and iron bars by an anti-gay mob, which aimed to "cleanse" homosexuality from a neighbourhood of Nigeria's capital Abuja.
Four of the victims were marched to a police station, where they were allegedly kicked and punched by police officers, according to Ifeanyi Orazulike of the International Center on Advocacy for the Right to Health.
Orazulike said he received an email from a colleague who said he was hiding from a mob of 40 people who struck around 1am Thursday, going from house to house saying their mission was to "cleanse" the area of gays.
Orazulike said he drove from his home at 4am to save the man in Gishiri, near central Abuja.
Dorothy Aken'Ova, executive director of Nigeria's International Centre for Reproductive Health and Sexual Rights, said she stayed up all night Wednesday trying to get police and Civil Defence to send officers to the scene after she got a phone call from a man who was being attacked.
"Instead of helping them, apparently some of them were arrested," she told AP.
"None of the [law enforcement] agents responded to our distress calls."
Nigerian President Goodluck Jonathan has recently signed the Same Sex Marriage (Prohibition) Bill 2013 - the so-called "Jail the Gays" bill - which imposes prison sentences of up to 14 years on those found guilty of involvement in a gay marriage or civil union.
Anyone who registers, operates or takes part in gay organisations, or who makes a public show of a same-sex relationship can face to up to 10 years in prison.
"Since the Same Sex Marriage (Prohibition) Act was signed, we have expressed concern as a friend of Nigeria that it might be used by some to justify violence against Nigerians based on their sexual orientation," the US Embassy said in a statement Friday. "Recent attacks in Abuja deepen our concern on this front."
Two Islamic courts in the Nigerian city of Bauchi have been forced to suspend the trials of 13 men accused of homosexuality, following a wave of protests.
Demonstrators gathered outside one court and threw stones at the building, demanding summary trial and execution for the 10 defendants.
The same court had earlier convicted a man of homosexual offences and given him 20 lashes.