Flintlock, military manoeuvres in Jacqueville U.S. President Donald Trump has accused Nigeria of failing to protect Christians from Islamist militants in the northwest.
Nigeria denies discriminating against any religion, saying its security forces target armed groups that attack both Christians and Muslims.
The U.S. carried out strikes targeting Islamic State-linked militants in December, and a small U.S. military team has been operating on the ground to boost Nigeria's intelligence capabilities.
In recent days, several planes carrying U.S. troops and equipment have headed to Nigeria's northern states, according to flight tracking data reviewed by Reuters.
Major General Samaila Uba, spokesperson for Nigeria's Defence Headquarters, said the troops would train and advise local forces, but not take part in combat.
Earlier this month, Nigeria's military said it expected around 200 more U.S. troops.
Presidential spokesperson Sunday Dare said Nigeria needed "massive support from the U.S. government" in terms of fighter jets and munitions, but declined to give numbers or a timeframe.
Nigeria's 240 million people are evenly split between Christians mainly in the south and Muslims mainly in the north.
It acknowledges serious security problems, including from Islamist fighters, but denies that Christians face widespread or systematic persecution.
(Reporting by Jessica Donati, and MacDonald Dzirutwe in Lagos; Editing by Timothy Heritage and Kevin Liffey)