The hearing to determine whether Mercedes and Pirelli broke Formula One rules by holding in-season tyre tests has opened in Paris.

The International Automobile Federation (FIA) convened the international tribunal hearing to determine whether Mercedes gained a competitive advantage from the testing session in Barcelona last month.

An FIA inquiry determined the testing may have broken its rules, which ban the use of current-season cars for such tests.

Red Bull and Ferrari protested about the testing.

Pirelli denied any rules-breach and said the 1,000 kilometres of testing offered no advantages to Mercedes.