BARCELONA, Spain — King Felipe VI of Spain stepped forcefully into the political crisis over Catalonia on Tuesday, accusing the region’s separatist leaders of “inadmissible disloyalty” and of creating “a situation of extreme gravity” that threatened the country’s constitution and unity.

The monarch’s televised address came at the close of a daylong general strike in Catalonia, as well as road blockades and a mass rally in downtown Barcelona, to protest Sunday’s police crackdown on voters as they took part in an independence referendum that had been declared illegal by Spain’s constitutional court.

The Catalan authorities “have put themselves completely on the sidelines of the law and democracy,” Felipe said. “With their irresponsible conduct, they can even put at risk the economic and social stability of Catalonia and the whole of Spain.”