The Spanish government on Friday dismissed a letter from Catalan leaders offering talks over their looming independence referendum as "a trap", and announced it would intervene in Catalonia's finances to ensure that "not one euro" of public money was used to fund the "illegal" vote.

Sixteen days out from the planned referendum on October 1, Catalan President Carles Puigdemont and other top officials including the mayor of Barcelona released a letter appealing for an agreement on a vote and issuing "a new call to dialogue" without preconditions.

In the letter, addressed to Spanish Prime Minister Mariano Rajoy and King Felipe VI and carried by a number of media, the leaders said they were seeking talks "to make possible what in democracy is never a problem nor still less a crime: to listen to the voice of the citizens".

But the overture was roundly rebuffed by the spokesman for the Spanish government, Íñigo Méndez de Vigo, who said Madrid had not received the letter and only learned about it through the press.