President Trump vowed on Monday to be an active partner to Nigeria as the country battles extremist groups targeting Christians in Africa.

"We've had very serious problems with Christians who have been murdered, killed in Nigeria," Trump said during an Oval Office meeting with Nigerian President Muhammadu Buhari.

Trump said his administration plans to work "very hard" to combat Christian persecution by "terrible" groups like Boko Haram. The Sunni terrorist organization has killed and kidnapped hundreds of African Christians in the past decade, often by bombing or burning churches in the region.

Earlier this year, members of the militant group raided a girls' school in northeastern Nigeria and kidnapped 110 students. One of the girls, 15-year-old Leah Sharibu, has remained captive reportedly because of her refusal to convert from Christianity to Islam.

"My daughter is alive, but they wouldn't release her because she is Christian," her father told reporters earlier this month. "They told her they would release her if she converted, but she said she will never become a Muslim. I am very sad, but I am also overjoyed because my daughter did not denounce Christ."

Trump's meeting with Buhari on Monday comes nearly a year after he approved the sale of a dozen military aircraft to Nigeria to help the country fight Boko Haram. The deal was worth nearly $600 million.

"We have met before, we have developed a great relationship. I look forward to our discussion today, very important, again, especially as it relates to terrorism," Trump said.