US President Donald Trump has ordered the military to prepare for action in Nigeria to tackle Islamist militant groups, accusing the government of failing to protect Christians.

Trump did not say which killings he was referring to, but claims of a genocide against Nigeria's Christians have been circulating in recent weeks and months in some right-wing US circles.

Groups monitoring violence say there is no evidence to suggest that Christians are being killed more than Muslims in Nigeria, which is roughly evenly divided between followers of the two religions.

An advisor to Nigeria's president told the BBC that any military action against the jihadist groups should be carried out together.

Daniel Bwala said Nigeria would welcome US help in tackling the Islamist insurgents but noted that it was a "sovereign" country.

He also said the jihadists were not targeting members of a particular religion and that they had killed people from all faiths, or none.

Nigeria's President Bola Tinubu has insisted there is religious tolerance in the country and said the security challenges were affecting people "across faiths and regions".

Trump wrote in a social media post on Saturday that he had instructed the US Department of War to prepare for "possible action".

He warned that he might send the military into Nigeria "guns-a-blazing" unless the Nigerian government intervened, and said that all aid to what he called "the now disgraced country" would be cut.

Trump added: "If we attack, it will be fast, vicious, and sweet, just like the terrorist thugs attack our CHERISHED Christians!"

US Defence Secretary Pete Hegseth replied to the post by writing: "Yes sir.

"The Department of War is preparing for action. Either the Nigerian Government protects Christians, or we will kill the Islamic Terrorists who are committing these horrible atrocities."

Trump's threat has triggered alarm across Nigeria. Many on social media are urging the government to step up its fight against Islamist groups to avert a situation where foreign troops are sent into the country.

But Mr Bwala, who said he was a Christian pastor, told the BBC's Newshour programme that Trump had a "unique way of communicating" and that Nigeria was not taking his words literally.

"We know the heart and intent of Trump is to help us fight insecurity," he said, adding that he hoped Trump would meet Tinubu in the coming days to discuss the issue.

Trump earlier announced that he had declared Nigeria a "Country of Particular Concern" because of the "existential threat" posed to its Christian population. He said "thousands" had been killed, without providing any evidence.

This is a designation used by the US State Department that provides for sanctions against countries "engaged in severe violations of religious freedom".

Following this announcement, Tinubu said his government was committed to working with the US and the international community to protect communities of all faiths.

"The characterisation of Nigeria as religiously intolerant does not reflect our national reality," the Nigerian leader said in a statement.

Jihadist groups such as Boko Haram and Islamic State West Africa Province have wrought havoc in north-eastern Nigeria for more than a decade, killing thousands of people - however most of these have been Muslims, according to Acled, a group which analyses political violence around the world.

In central Nigeria, there are also frequent clashes between mostly Muslim herders and farming groups, who are often Christian, over access to water and pasture.

Deadly cycles of tit-for-tat attacks have also seen thousands killed, but atrocities have been committed on both sides and human rights group say there is no evidence that Christians have been disproportionately targeted.

Trump has frequently expressed satisfaction over not having embroiled the US in a war during his tenure, and has cast himself as a peace-making president.

But the Republican leader is facing a growing number of voices domestically, particularly from the political right, who have drawn attention to the situation in Nigeria.

Additional reporting by Chris Ewokor in Abuja