"Spain is an independent and sovereign country that includes the Catalan region," Ban told four Spanish newspapers, El Pais, El Mundo, ABC and La Vanguardia.
"It is in this way that it was admitted to the United Nations and acts within the international community," he said, according to a Spanish translation of his comments published by El Pais.
Pro-independence parties in the wealthy northeast Spanish region are seeking to pass a resolution in the Catalan parliament in early November announcing the formal start of secession from Spain and the formation of a new republican state within 18 months.
The separatists won a majority of seats in the Catalan parliament in Barcelona for the first time in elections last month.
But Prime Minister Mariano Rajoy said Friday that Spain's main parties will work together to defend national unity against the independence drive.
Ban said the UN did not recognise Catalonia as a non-autonomous territory that should be able to claim the right to self-determination.
"When one speaks of self-determination, certain areas have been recognised by the United Nations as non-autonomous territories. But Catalonia does not fall into this category," he told the Spanish press.
"A positive aspect of Spain is that there is respect for diversity: the culture, the languages, the traditions," he added.
While they now control a majority of seats in the regional parliament, the Catalan separatists won less than half of the vote in last month's elections, raising questions over the legitimacy of their latest push for independence.
Ban expressed hope for "a consensual solution" for Catalonia, "based on dialogue and conforming to the democratic tradition".
"I ask leaders and the Catalan people to engage in the dialogue," he said, ahead of general elections due in Spain on December 20.
Catalans' longstanding demands for greater autonomy have intensified in recent years, in tandem with the country's economic crisis.
Home to 7.5 million people, Spain's richest region has its own widely spoken language and distinct culture.