The Vatican has dismissed as a heretic a mystical medieval monk apparently cited by Barack Obama as a moral authority and visionary.

According to Father Raniero Cantalamessa, preacher to the Pontifical Household, the US President referred in campaign speeches to Gioacchino da Fiore, or Joachim of Fiore, as a ''master of contemporary civilisation'' who had sought to create a better world. Drawing on the Book of Revelation, Gioacchino envisaged a "new age of the Holy Spirit" in which the Church hierarchy would cease to exist and Christians would unite with infidels in an "Order of the Just".

Dante refers to Gioacchino da Fiore, who lived from 1130 to 1202, as a ''gifted prophet'' in The Divine Comedy, and claimed that miracles occurred to those who prayed at his tomb. His followers have applied to the Vatican for him to be officially beatified, the step before sainthood.

However, Father Cantalamessa said: ''Few of those who expound on Gioacchino da Fiore on the internet know, or go to the trouble of finding out, what this character really said." In the latest of a series of Lenten lectures for Pope Benedict XVI and the papal household, he said that, according to ''vogueish'' interpretations, the monk had proposed a "liberal and spiritual Church" able to move beyond dogmas and hierarchies. However, Gioacchino's views were ''false and heretical'', Father Cantalamessa said, since Christian believers were guided not only by the spirit but also by the laws of the Church. "It can be fatal to do without one or the other of these guides.''

He said that Mr Obama had quoted Gioacchino three times during his Presidential campaign, thus "reviving interest in his doctrines", not least on the internet. But Gioacchino's theory that a "third age" would follow that of God the Father in the Old Testament and Jesus Christ in the New Testament was heretical, because it "strikes at the heart" of Christian belief in the Holy Trinity of Father, Son and Holy Spirit. Quoting the prophet Isaiah, St Matthew and St Paul, he said the accepted Christian doctrine was that the Holy Spirit existed at the same time as the period of the Old and New Testaments, inspiring both the ancient prophets and Jesus Christ.

Gioacchino da Fiore was the founder of the monastic order of San Giovanni in Fiore, whose followers are called Joachimites. Born near Cosenza in Calabria, he became a notary but underwent a spiritual crisis after a pilgrimage to the Holy Land, and lived as a hermit on his return to Italy.

He joined a Cistercian abbey as a lay brother and was later ordained, devoting himself to uncovering hidden meanings in the Scriptures, above all the Book of Revelation. He eventually founded his own abbey at Fiore in the Calabrian mountains as a branch of the Cistercian Order, with papal approval.

He was criticised, however, by St Thomas Aquinas in his Summa Theologica, and Pope Alexander IV (reigned 1254-61) condemned his writings, setting set up a commission which eventually declared his theories heretical.

Italian reports said officials in Calabria had invited Mr Obama to visit the abbey at San Giovanni in Fiore in the National Park where Joachim of Fiore is buried, and had offered to make the President an honorary citizen of the local town. "We are ready to welcome Obama," Antonio Nicoletti, the mayor of San Giovanni in Fiore, said.