He was asked if he envisioned troops on the ground or air strikes in Nigeria, by reporters aboard Air Force One.
"Could be. I mean, other things. I envisage a lot of things. They're killing record numbers of Christians in Nigeria," he said.
"They're killing the Christians and killing them in very large numbers. We're not going to allow that to happen."
Trump made the comment on Sunday evening as he headed back to Washington after spending the weekend in Florida.
Trump threatened on Saturday to take military action against Nigeria if Africa's most populous country failed to crack down on the killing of Christians.
The threat of military action came a day after his administration added Nigeria back to a "Countries of Particular Concern" list of nations that the US says have violated religious freedoms.
Other nations on the list include China, Myanmar, North Korea, Russia and Pakistan.Nigeria says it would welcome US help in fighting Islamist insurgents as long as its territorial integrity is respected.
An adviser to Nigerian President Bola Tinubu, responded earlier the the threats of military action.
"We welcome US assistance as long as it recognises our territorial integrity," Daniel Bwala, Tinubu's advisor told Reuters.
Bwala sought to play down tensions between the two states, despite Trump calling Nigeria a "disgraced country".
"We don't take it literally, because we know Donald Trump thinks well of Nigeria," Bwala said.
"I am sure by the time these two leaders meet and sit, there would be better outcomes in our joint resolve to fight terrorism," he said.
Nigeria, a country of more than 200 million people and around 200 ethnic groups, is divided between the largely Muslim north and mostly Christian south.
Islamist insurgents such as Boko Haram and Islamic State West Africa Province have wrought havoc in the country for more than 15 years, killing thousands of people, but their attacks have been largely confined to the northeast of the country, which is majority Muslim.
While Christians have been killed, the vast majority of the victims have been Muslims, analysts say.
In central Nigeria there have been frequent clashes between mostly Muslim herders and mainly Christian farmers over access to water and pasture, while in the northwest of the country, gunmen routinely attack villages, kidnapping residents for ransom.
Nigeria "does not discriminate against any tribe or religion in the fight against insecurity", Bwala said.
"There is no Christian genocide."
