(CNN) -- A former Catholic bishop in Norway has admitted sexually abusing a minor 20 years ago, a spokesman for the Norwegian Catholic Church said Wednesday.

Bishop Georg Mueller admitted to having sexually abused an altar boy but said there were no other victims, said church spokesman Andreas Dingstad.

Mueller, 58, became a priest in 1978 and served as bishop of Trondheim, Norway, from 1997 to 2009. The abuse is said to have happened more than 20 years ago, when Mueller was a priest in Trondheim, Dingstad said.

Allegations of sexual abuse by Catholic priests have spread across Europe, surfacing in countries including the Netherlands, France, Mexico, Italy, Ireland, the United States, Austria and Germany, home country of Pope Benedict XVI.

Some have been critical of Catholic leaders including the pope, saying little action had been taken when he was a top Vatican official.

Waves of victims have come forward, claiming they were victims of abuse by religious leaders and saying the church did little or nothing to stop it.

In a rare move, a senior cardinal spoke Sunday before the pope's Easter Mass at the Vatican, saying the pontiff maintains the support of Catholics around the world "who do not let themselves be influenced by the gossip."

Cardinal Angelo Sodano, former Vatican secretary of state and dean of the College of Cardinals, did not specifically mention the sexual abuse scandal, but his remarks clearly referred to criticism leveled at church leaders.

The pope did not address the scandal in his Easter message. In a letter last month, he said he was "truly sorry" for the abuse suffered by victims at the hands of Catholic priests in Ireland.