The US has sent a small team of troops to Nigeria, the general in charge of the US command for Africa said on Tuesday, the first acknowledgment of US forces on the ground since Washington struck by air on Christmas Day.
President Donald Trump ordered airstrikes on what he described as Islamic State (ISIS) targets in Nigeria in December and said there could be more US military action there.
Reuters earlier reported that the US had been conducting surveillance flights over the country from Ghana since at least late November.
The top general said the US team was sent after both countries agreed that more needed to be done to combat the terrorist threat in West Africa.
"That has led to increased collaboration between our nations to include a small US team that brings some unique capabilities from the United States," General Dagvin R.M. Anderson, head of the US military's Africa Command AFRICOM, told journalists during a press briefing on Tuesday.
Anderson did not provide further details about the size and scope of their mission.
Defense Minister Christopher Musa confirmed that a team was working in Nigeria but did not provide further details.
Aiding Nigerian forces
A former US official said the US team appeared to be heavily involved in intelligence gathering and enabling Nigerian forces to strike terrorist-affiliated groups.
Nigeria has come under intense pressure by Washington to act after President Trump accused the West African nation of failing to protect Christians from terrorists operating in the northwest.
The Nigerian government denies any systematic persecution of Christians, saying it is targeting Islamist fighters and other armed groups that attack both Christian and Muslim civilians.
Boko Haram and Islamic State West Africa Province (ISWAP) fighters have intensified attacks on military convoys and civilians, and the northwest remains the epicentre of the 17-year Islamist insurgency.
The US military’s Africa Command said the strike was carried out in Sokoto state in coordination with Nigerian authorities and killed multiple ISIS terrorists.
The strike came after 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.