A former missionary will serve up to 40 years in prison after he was found guilty by a U.S. federal court of sexually abusing children at an orphanage in Kenya.

Matthew Lane Durham, 21, was charged with molesting eight kids at the Upendo Children's in Nairobi in 2014, according to Reuters.

During the sentencing, Durham said he does not fear God's judgment.

"Judgment from God is central, not the judgment of man. I do not fear God's judgment," he said.

Durham, who is from Edmond, Oklahoma, denied molesting the children but at the preliminary hearing, he told Upendo personnel that he thought he had been possessed by evil spirit and he did not remember molesting the children.

Young victims said Durham touched them sexually or told them to touch themselves while he watched.

Durham allegedly confessed to the founder of Upendo and church members that he raped and sexually abused the children.

In June last year, a federal jury found him guilty on seven counts of engaging in illicit sexual conduct with the children. But last January, U.S. District Judge David Russell acquitted him on three of the seven counts as the judge felt the prosecutors failed to establish that the suspect engaged in sexual act with the victim in the counts.

Durham had previously pleaded not guilty to 17 charges.

Prosecutors said Durham used his position as a missionary to prey upon the victims but his lawyer said his handwritten and taped confessions were coerced.

Russell said Durham is a serial rapist and "kids' worst nightmare."

According to the U.S. Justice Department, Duham was a volunteer at the orphanage, which specialises in assisting neglected Kenyan children by providing them food, housing, clothes, school and religion.

Evidence showed that between April 30, 2014 and June 17, 2014, Durham travelled from Oklahoma City to Nairobi and while at the orphanage, he engaged in illicit sexual conduct with seven children.