Pope Francis delivers a speech during a meeting with youth of the diocese on July 5, 2014 in Castelpetroso, southern Italy, as part of his one day visit in the Molise region. AFP PHOTO / ANDREAS SOLARO (Photo credit should read ANDREAS SOLARO/AFP/Getty Images)

CAMPOBASSO, Italy, July 5 (Reuters) - Pope Francis called for more respect for nature on Saturday, branding the destruction of South America's rain forests and other forms of environmental exploitation a sin of modern times.

In an address at the university of Molise, an agricultural and industrial region in southern Italy, Francis said the Earth should be allowed to give her fruits without being exploited.

"This is one of the greatest challenges of our time: to convert ourselves to a type of development that knows how to respect creation," he told students, struggling farmers, and laid-off workers in a university hall.

"When I look at America, also my own homeland (South America), so many forests, all cut, that have become land ... that can longer give life. This is our sin, exploiting the Earth and not allowing her to her give us what she has within her," the Argentine pope said in unprepared remarks.

Francis, who took his name from Francis of Assisi, the 13th century saint seen as the patron of animals and the environment, is writing an encyclical on man's relationship with nature.

Since his election in March, 2013, the leader of the world's 1.2 billion Roman Catholics has made many appeals in defense of the environment.

After the university meeting, Francis said mass for tens of thousands of people in a stadium. (Reporting by Philip Pullella; Editing by Raissa Kasolowsky)