The Pope's first visit to France since his election has fuelled debate on church-state relations in a country which prides itself in keeping faith and politics strictly separate.

Last Friday, President Nicolas Sarkozy and his wife Carla Bruni broke with tradition by greeting the Pope at the airport. Bucking decades of staunchly secularist presidents, lapsed Catholic Mr Sarkozy said that religious "values" should play a greater role in public life.

Mr Sarkozy previously stirred up controversy when he called for a "positive secularism" that would make more space for religion in the public realm during a visit to the Vatican last year. The separation of church and state has been enshrined in French law since 1905.

The Pope sought to quell the row during an open-air mass at Lourdes on Sunday.

"The church does not claim the state's place. She does not want to substitute it," he told pilgrims.

He added, however, that France should "bring to the fore" its Christian roots to "enable each inhabitant to better understand his country".

At least 100,000 pilgrims stood in a sodden field to hear the Pope speak on the 150th anniversary of visions of the Virgin Mary to a 14-year-old peasant girl, Bernadette Soubirous.

The Pope urged the pilgrims not to lose hope in the face of challenges.

"The power of love is stronger than the evil which threatens us," he said, later adding, "Do not allow yourselves to be discouraged by difficulties."