The United States has withdrawn most of the troops it deployed to Nigeria earlier this year in an effort to help combat Islamist militant groups.

In December, U.S. and Nigerian forces launched a joint operation in the Lake Chad Basin area, which included strikes against militants on Christmas Day, followed by the deployment of about 200 troops two months later.

Senior Islamic State (IS) leader Abu-Bilal al-Minuki was killed during the months-long mission.

On Thursday, the United States said the operation had been a success, while Nigeria’s military spokesman told the BBC that the withdrawal of American soldiers “would not affect our momentum in any way.”

Despite the operations, jihadist groups continue to carry out attacks, especially in northeastern Nigeria.

Maj. Gen. Michael Onoja said intelligence sharing between the two countries would continue, which the US military also said in its report.

Military cooperation between Nigeria and the United States increased after Washington accused Nigerian authorities of not doing enough to protect vulnerable groups against Islamist militants and alleged there was a “Christian genocide” in the country.

Nigeria has firmly rejected this claim, saying the violence is complex and affects people from all communities.

Organizations that monitor political violence in Nigeria say that most victims of jihadist groups are Muslims because they operate mainly in the north of the country, where most people follow Islam.