Hannah McKay/Reuters
Catalan authorities "have placed themselves outside the law and democracy, they have tried to break the unity of Spain and national sovereignty," he said, according to a translation by the Financial Times.
It was the "responsibility of the legitimate powers of the state to ensure the constitutional order," he added.
ABC News reported that he also said the bid by authorities in Catalonia to push ahead with independence has "undermined coexistence" in the region.
The king's comments follow protests that broke out Tuesday across Catalonia, a region in the country that includes Barcelona, over the crackdown by Spanish police during the vote over the weekend. The attempt to stop the vote came after Spain's Constitutional Court ruled that the referendum violated the country's constitution because it "does not recognize the right to self-determination and establishes that sovereignty resides with Spanish citizens collectively," according to the Washington Post.
According to data from BBC, nearly 900 people were hurt in the melee that followed. Still, turnout for the vote was 43%, and about 90% of voters were in favor of splitting from the rest of the country.
The Spanish government took a strong stance against the referendum ahead of the vote by raiding offices, shutting down pro-independence websites, and arresting officials. Some analysts argued that the recent crackdown only helped further unite the pro-independence groups in Catalonia.
Catalonia, which has its own language and culture, is one of Spain's economic powerhouses. It contributes nearly one-fifth of the country's total GDP and has an economy larger than that of Portugal.