VATICAN CITY, June 17 (Reuters) - Pope Francis on Wednesday called for respect for migrants and suggested that "people and institutions" who close doors to them should seek forgiveness from God.

The pope's appeal, made at the end of his weekly general audience, came a growing debate in Europe on how to deal with an immigrant crisis that has included clashes at the French-Italian borer between police and migrants.

"I invite you all to ask forgiveness for the persons and the institutions who close the door to these people who are seeking a family, who are seeking to be protected," he said in unscripted remarks delivered in a sombre voice.

France and Austria have stepped up border controls on migrants coming from Italy, turning back hundreds and leaving growing numbers camped out in railway stations in Rome and Milan.

In a sign of persisting discord over how to deal with the migrant crisis, Italian Prime Minister Matteo Renzi threatened retaliation if other EU countries did not agree to take their fair share of refugees that land on Italy's shores.

The pope said "these brothers and sisters of our are seeking refuge far from their lands, they are seeking a home where they can live without fear."

He asked for prayers that their "human dignity always be respected" and urged the international community to "work together and efficiently to prevent the causes of forced migration".

France, Italy and Germany agreed on Tuesday to join forces to identify migrants arriving by sea and to swiftly relocate them across the European Union or send them back to their home countries if their claims for asylum in Europe are rejected.

As they deliberated, police began removing mainly African migrants from makeshift seaside camps on the Italian-French border. Around 300 had collected on the Italian side in hopes of proceeding into France and onwards to northern Europe where relatives live and job chances might be better. (Reporting by Philip Pullella; Editing by Tom Heneghan)