A Roman Catholic monsignor who covered up sex abuse claims against priests in the US has been jailed for three to six years.

Lynn was the former secretary for clergy at the Archdiocese of Philadelphia.

Lynn handled priest assignments and child sexual assault complaints from 1992 to 2004. A jury convicted him last month of child endangerment for his oversight of now-defrocked priest Edward Avery, who is serving up to five years in prison.

Lynn's lawyers sought probation and have vowed to appeal.

The 61-year-old Lynn was acquitted of conspiracy and a second endangerment count.

Judge Teresa Sarmina said Lynn enabled "monsters in clerical garb ... to destroy the souls of children, to whom you turned a hard heart."

She added: "You knew full well what was right, Monsignor Lynn, but you chose wrong."

In 1992, a doctor told Lynn's office that Avery had abused him years earlier. Lynn met the doctor and sent Avery for treatment, but the church--run facility diagnosed him with an alcohol problem, not a sexual disorder. Avery was returned to ministry and sent to live at the parish where the altar boy was assaulted in 1999.

"I did not intend any harm to come to (Avery's victim)," Lynn said. "My best was not good enough to stop that harm."

Prosecutors who spent a decade investigating sex abuse complaints kept in secret files at the archdiocese argue that Lynn and unindicted co-conspirators in the church hierarchy kept children in danger.