About 100 US soldiers have arrived in Nigeria to train the West African nation's armed forces and help them with intelligence in their battle against growing security threats from Islamist militants and other armed groups.

The troops and equipment had landed at an airfield in the north-eastern state of Bauchi, Nigerian defence spokesperson Maj Gen Samaila Uba said.

He reiterated that the US personnel would not be engaging in combat operations and had come at the request of the government.

This is the latest sign of military co-operation between the two countries following the Christmas Day airstrikes launched by the US on two camps run by an Islamist militant group in north-western Nigeria.

The government said it had asked for help in tackling Islamist militant groups such as Boko Haram, Islamic State in West Africa Province (Iswap) as well as other groups.

Nigeria faces an array of security challenges including an Islamist insurgency, attacks by criminal gangs - known locally as "bandits" who loot and kidnap for ransom - clashes over land and separatist unrest.

"The collaboration will provide access to specialised technical capabilities aimed at strengthening Nigeria's ability to deter terrorist threats and enhance the protection of vulnerable communities across the country," Maj Gen Samaila Uba said in a statement.

The deployment came after discussions between Nigerian and US defence officials during a working group, he explained.

It also follows confirmation earlier this month by the US Africa Command that a small team of American forces was already operating in the country. Nigerian military officials had previously indicated that around 200 additional troops were expected.

Late last year, the administration of US President Donald Trump raised concerns about the treatment of Christians in Nigeria - and urged the government to do more to improve security and strengthen protection for Christian communities.

Trump had previously claimed there was a "Christian genocide" under way in Nigeria - an allegation strongly rejected by Nigeria's government, which said Muslims, Christians and people of no faith were victims of attacks.

Nigeria's government has expressed its thanks for US aid in tackling security issues and emphasised the strikes on 25 December, which targeted an Islamist militant group called Lakurawa in the northern-western state of Sokoto, were approved by President Bola Tinubu.

There are more than 250 ethnic groups in Nigeria, which is roughly divided into a mainly Muslim north, a largely Christian south, with intermingling in the middle.