President Donald Trump said there could be more strikes by the US in Nigeria if Christians are killed in the African nation, even as Nigeria has previously denied Christians there are subjected to systematic persecution.

Trump's comments in an interview with the New York Times were published on the newspaper's website on Thursday.

Trump made the remarks when asked about Washington's Christmas Day military strike in Nigeria. The US military said at the time it carried out a strike against Islamic State militants in northwest Nigeria at the request of Nigeria's government.

Nigeria said then that the strike was a "joint operation" targeting "terrorists," and had "nothing to do with a particular religion."

"I'd love to make it a one-time strike ... But if they continue to kill Christians, it will be a many-time strike," Trump was quoted as saying.

When asked about his own Africa adviser having said that Islamic State and Boko Haram militants were killing more Muslims than Christians, Trump responded: "I think that Muslims are being killed also in Nigeria. But it's mostly Christians."

Trump, in late October, began warning that Christianity faces an "existential threat" in Nigeria and threatened to militarily intervene in the West African country over what he says is its failure to stop violence targeting Christian communities.

Nigeria's population of over 230-million people is roughly evenly divided among Christians, who predominate in the south, and Muslims, who predominate in the north.

While Nigeria has had persistent security problems, including violence and kidnappings by Islamist insurgents in the north, it strongly denies that Christians are subjected to systematic persecution.

Its government responded to Trump's past threats by saying it intended to work with Washington against militants, while rejecting US language that suggested Christians were in particular peril. Nigerian authorities note that militants have killed many Muslims as well as Christians.