The Vatican was last night at the centre of an unusually public sex scandal after acknowledging it had suspended a senior official who was filmed apparently propositioning a young man in his office.

Monsignor Tommaso Stenico, a capo ufficio, or section head, at the Vatican ministry responsible for the clergy, insisted yesterday he was not gay. He said he had posed as a homosexual to research a plot by satanists.

The affair is the latest of several indications that the traditional immunity enjoyed by the Catholic church in Italy over sex scandals is gradually giving way.

The Pope's spokesman, Father Federico Lombardi, said on Saturday he was unable to deny rumours that the Vatican had suspended one of its top bureaucrats following a report shown on Italian television. A few hours later a website identified the official as Mgr Stenico, a 60-year-old official who ranks joint third in the hierarchy of his department, known as the Congregation for the Clergy.

A programme broadcast on October 1 by La7 - the only national channel not owned by Silvio Berlusconi or the state - included a sequence it said had been filmed secretly in a Vatican office. The six-minute sequence was said to have been captured by a young man who had come into contact with a Vatican official via an internet chatroom.

He was invited to have sado-masochistic sex and arrangements were made for a meeting in St Peter's Square. Unknown to the older man, the other man, who said he wanted to expose the hypocrisy of the Catholic church, arrived equipped with concealed video and audio recording equipment.

Television viewers saw the Vatican official sit alongside his guest and say: "You're very good-looking."

"Thank you," replied the younger man, before putting it to his host that he was about to commit a sin.

"I don't feel it is a sin," said the official. When the other man insisted that it was at odds with the teaching of the church, the Vatican official brought the conversation to an abrupt end.

When his guest bade farewell, saying "It's been a pleasure," the Vatican official replied: "Not for me, because you don't fancy me."

Mgr Stenico acknowledged in several Italian media interviews yesterday that he had been suspended.

But he told the Corriere della Sera newspaper that he "wanted to carry out a study, probably for publication". He said he was a registered psychologist and psychotherapist and his aim had been "to study how priests are ensnared".

He added: "I really believe that there is a diabolic plan by satanist groups who take aim at priests."

Father Lombardi said the Vatican had to act with the decisiveness and severity called for by behaviour incompatible with priestly service and the Holy See. Mgr Stenico's case is expected to be judged by a special tribunal of the Congregation for the Doctrine of the Faith.

It is the latest of several recent embarrassments for the Catholic church in Italy. One of its best-known priests, renowned for his care of drug addicts, is being investigated for sex abuse. And prosecutors in both Turin and Siena are looking into claims of sex abuse and financial wrongdoing by senior church officials.