By Mark Lowen
BBC News, Belgrade
Around 30 million are estimated to have visited since the first sighting
The Vatican has announced a commission to investigate claims that the Virgin Mary appears on a daily basis in a town in Bosnia-Hercegovina.
Six children first reported the apparition in the town of Medjugorje in June 1981.
However, the sightings have not yet received official recognition from the Catholic Church.
The 20-strong commission will report to the Congregation for the Doctrine of the Faith, the top doctrinal body.
For almost 30 years, the Virgin Mary has been said to appear daily in Medjugorje, dressed sometimes in a grey dress and veil and sometimes in gold, crowned with stars and floating on a cloud.
It is said she speaks in Croatian, uttering the words: "I've come because there are many true believers here. I wish to be with you to convert and reconcile the whole world."
It is also said that three flashes of light precede her apparitions, during which the voices of the visionaries can no longer be heard.
But the Catholic Church has long debated the credibility of the sightings.
There was a recent visit by a cardinal from Vienna, Christoph Schoenberg.
But the bishop of neighbouring Mostar has frequently criticised unquestioning belief in the claims.
Until the commission reports back to the Church's top doctrinal body, believers are likely to continue to flock to this small Bosnian town.
Around 30 million are estimated to have visited since the first sighting of what they call "Our Lady".