The Spanish government has called on Catalan president Carles Puigdemont to present his proposal for a regional independence referendum before Parliament because the issue affects all of Spain and would require a change in the country's constitution.

Deputy Prime Minister Soraya Saenz de Santamaria made the offer Friday in apparent response to complaints by Puigdemont that Spain refuses to discuss his regional government's secession demands.

The government says it cannot permit a secession referendum as it is unconstitutional.

Relations between the central and regional governments have soured greatly over the issue.

Puidgemont is to speak on the issue Monday at a private conference in Madrid's town hall that has triggered protests.

Catalonia, which represents a fifth of Spain's GDP, insists it will hold the vote in September.