Pope Francis expressed serious doubts regarding reported daily apparitions of the Virgin at Medjugorje in Bosnia, a site which attracts a million pilgrims annually.
In June 1981, six Bosnian children and teenagers said they had witnessed the appearance of the Virgin in the southern town, and allege she continues to visit to this day.
The woman they saw "is not the mother of Jesus," the Pope said Saturday aboard the papal plane on his return from a trip to Portugal, where he canonised two young shepherds who had visions of the Virgin 100 years ago.
The Pope said an investigation under way by the Church had thrown up doubts regarding the Medjugorje apparitions.
He said he preferred "'the Mother Madonna' or 'our Mother', and not the 'Madonna chief of service', for sending daily messages."
The remarks are likely to make waves in Bosnia, where Catholics make up about 10 percent of the population and the religious tourism at Medjugorje brings money into the poor Balkan country.
"These supposed apparitions don't have much value -- I'm giving my personal opinion," the pontiff continued.
"But it is obvious, who thinks the Virgin would say: 'come to this place tomorrow at this time and I'll give a message to a seer'?"
However the Pope was more circumspect about the original 1981 apparitions, which he didn't immediately reject.
"On the original apparitions, the ones the children had, the enquiry says, more or less, that investigations need to continue," he said.
Several investigations have already been carried out, the last in January 2014, but the Pope had made no announcement since.
However, in November 2013, he did express some doubts.
"The Virgin," he said, "is not a chief of the post office who would send messages every day."
The Vatican earlier this year sent a new envoy to "acquire a deeper knowledge of the pastoral situation” in Medjugorje, and "above all the needs of the faithful who go there on pilgrimage".
The envoy, however, will not be tasked with verifying the authenticity of the apparitions, because that task falls to the Vatican’s Congregation for the Doctrine of the Faith.