U2 singer and African activist Bono says he came face-to-face with the terrorism of Boko Haram Islamic extremists on a recent trip to Nigeria.

“I have to admit I was not prepared to see a nine-year-old child bride,” the Irish singer told the German newspaper Welt am Sonntag.

The girl was surrounded by other child brides, the singer recounted.

“At that moment I knew I had come face-to-face with Boko Haram.”

Boko Haram poses an ongoing threat to communities in the northeast of Nigeria and has also launched offensives in neighbouring Chad, Niger and Cameroon.

The group’s goal is to enforce a strict interpretation of Islamic law, known as sharia.

Nigerian soldiers after an operation against Boko Haram terrorists in March. Photo: Getty

In 2014, Boko Haram kidnapped 276 girls and young women from their school dormitory in the north-eastern village of Chibok.

Only about 50 of the abductees managed to escape, while the rest are still believed to be held by Boko Haram, either as sex slaves or in forced marriages.

Bono also said action was needed to stop the humanitarian disaster in northeastern Nigeria.

“According to the United Nations, some 50,000 children face death by starvation.

“The UN needs $US300 million in aid. We have to help, and quickly,” Bono said.

With AAP