U.S. President Donald Trump has vowed to work "very, very hard" to prevent the attacks against Christians in Nigeria, where the government has been struggling to curb violence committed by extremist groups like Boko Haram and militant Fulani herdsmen.

During a meeting with Nigerian President Muhammadu Buhari at the White House on Monday, Trump expressed concern about the plight of Christians in the West African country.

"We have had very serious problems with Christians who are being murdered in Nigeria, we are going to be working on that problem very, very hard because we cannot allow that to happen," the U.S. president said, as reported by Nigerian news website The Cable.

At a joint press conference, Trump reportedly commended Buhari for taking part in the fight against the Islamic State and Boko Haram as he encouraged greater efforts to ensure the safety of civilians.

The Christian Association of Nigeria (CAN) called on all members to participate in a protest last week calling out the Nigerian government over its failure to stop the attacks.

Buhari assured Trump that he was working hard to address the violence in the country and thanked the U.S. government for providing weapons and training for the Nigerian military.

"We are even more grateful for the physical presence of the United States military who are training in our institutions and who also go to the front in the northeast to see how they are doing," the Nigerian president said, according to The Cable.

"The commitment of the United States to get rid of terrorism across the world, we have first hand experience of that and we are very grateful for it," he added.

"We encourage Nigeria and the federal state and local leaders to do everything in their power to immediately secure the affected communities and to protect innocent civilians of all faiths including Muslims and including Christians," Trump stated, according to Christianity Today.

The meeting between Trump and Buhari came after Christian groups held a nationwide protest to denounce the recent attack on a church in Nigeria's Benue state.

At least 19 people, including two priests, were shot dead when gunmen raided the St. Ignatius Catholic Church in Mbalom in late April. Nigerian officials suspected that the attacks were carried out by Fulani militants, who have been active mainly in Nigeria's "middle belt," where the majority-Christian south and majority-Muslim north meet.

Persecution watchdog group Open Doors has reported that attacks by Fulani militants have resulted in at least 611 deaths in the past year.

The organization's CEO, David Curry, accused the Nigerian government of turning a blind eye to the violence being perpetrated by the Fulani militants.

Curry called on the Nigerian government to "take tangible steps" to prevent further violence at the hands of the militants and appealed to international governments, including the U.S., to hold Nigeria accountable.

"We cannot ignore the unmistakable maliciousness of the militant Fulani herdsmen, just as we have come to recognize Boko Haram's signature cruelty," he said.

"Governments around the world must ask why these attacks are happening, and what the Nigerian government is doing to stop it."