* Pope prays before mysterious Shroud of Turin
* Some say shroud is Jesus's burial cloth, some say a fake
* Speaks of city's past as centre of devil worship, new snares (Recasts, adds more comments)
By Philip Pullella
TURIN, Italy, June 21 (Reuters) - Pope Francis prayed on Sunday before the mysterious shroud some Christians believe is Jesus's burial cloth but skirted the issue of its authenticity, saying it should remind people of all suffering and persecution.
On his first day of a visit to the northern industrial city of Turin, he defended migrants flocking to Europe to escape war and injustice, saying it "makes one cry" to see them mistreated.
He also spoke of the city's 19th century reputation as a centre of devil worship and anti-clericalism, saying today's young people faced new snares of high unemployment, drugs and unbridled consumerism.
Francis was the latest of many popes to view the shroud, which is usually kept locked out of sight and is on display for only the third time in 17 years. Over a million people have seen it in two months.
After praying for several minutes before the cloth that has baffled scientists for decades, he touched its glass case and moved on to say Mass for 60,000 people. There he said the Shroud should spur people to reflect not only on Jesus but also on "the face of every suffering and unjustly persecuted person."
The Roman Catholic Church has not taken an official position on the cloth bearing an image, reversed like a photographic negative, of a man with the wounds of a crucifixion.
It shows the back and front of a bearded man, his arms crossed on his chest. It is marked by what appear to be rivulets of blood from wounds in the wrists, feet and side.
Sceptics say it is a masterful medieval forgery and carbon dating tests in 1988 dated it between 1260 and 1390, but some have challenged the accuracy of those tests.
The pope began the day with an outdoor rally on the theme of workers rights and immigration. Turin's factories drew in waves of poor southern Italian peasants in the post-war period. Today it is home to migrants from developing countries and social tensions have increased along with unemployment.
"Immigration increases competition but migrants should not be blamed because they are the victims of injustice, of this throw-away economy, of wars," he said.
Departing from his prepared text, he added: "It makes one cry to see the spectacle of these days in which human beings have been treated like merchandise."
France and Austria have stepped up border controls on migrants trying to enter from Italy, turning back hundreds and leaving many camped out in train stations in Rome and Milan.
Francis has made immigration a top priority of his papacy. His first trip in 2013 was to the southern island of Lampedusa to pay tribute to the thousands of migrants who have died trying to cross the Mediterranean. (Editing by Tom Heneghan)