US President Donald Trump has ordered the preparation of plans for military action in Nigeria to tackle Islamist militant groups, accusing the government of not doing enough to halt the killing of 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.

The government of Africa's most populous nation has not responded to the threat of US military action.

However, Nigeria's President Bola Tinubu insisted that there was 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, warning that he might send the military into Nigeria guns-a-blazing unless the Nigerian government intervened. He also indicated that all aid to the 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!

Trump has characterized Nigeria as a Country of Particular Concern due to what he describes as an existential threat to its Christian population, claiming that thousands have been killed without providing evidence.

This characterization has prompted criticism, with Tinubu asserting that his administration is committed to collaborating with the US and the international community to provide security for all faiths.

Jihadist groups such as Boko Haram have been wreaking havoc in Nigeria for over a decade, affecting both Christians and Muslims. The ongoing violent clashes between predominantly Muslim herders and mainly Christian farmers further complicate the security landscape.

Despite Trump's claims, most analyses suggest that violence impacts both religious communities equally, with violations occurring on all sides.

Additional reporting by Chris Ewokor in Abuja.