France and Poland signed a treaty on Friday to increase cooperation on defence, nuclear energy and other measures, in a sign of growing alliances between European nations amid concerns about U.S. commitment to Europe's security.

Poland and France will guarantee each other's security under a new treaty signed in Nancy on May 9, Prime Minister Donald Tusk said. The agreement, which includes mutual military assistance, marks the first time France has extended such a commitment to a non-neighbouring country.

Such protection is of immense interest to Poland, which shares a border with Russia's exclave of Kaliningrad and warns that it too could face aggression.