European Union president Donald Tusk and his Polish counterpart Andrzej Duda on Monday urged "calm" after the EU launched an unprecedented probe to see if controversial legal changes in Poland violated democratic norms.

Duda, speaking alongside Tusk after a meeting in Brussels, said "what is needed is a calm dialogue with calmed-down emotions" while his host, a former Polish premier, repeatedly stressed the need for "restraint and a sense of reasonable language."