A day after hundreds of thousands of people marched in Barcelona to demand the release of separatist officials, Mariano Rajoy also urged businesses not to flee the wealthy northern region.
Hundreds of thousands of supporters of a unified Spain filled Barcelona's streets on Sunday in one of the biggest shows of force yet by the so-called silent majority that has watched as regional political leaders push for Catalan independence.
The wealthy region's intention to break away has plunged Spain into its worst political crisis since an attempted military coup in 1981, with Madrid threatening to sack the Catalan government if it goes ahead.
Catalan president Carles Puigdemont arrived at the regional parliament in Barcelona under the glare of cameras from around the world, ready to address lawmakers.
Hundreds of thousands of flag-waving demonstrators packed central Barcelona on Sunday to rally against plans by separatist leaders to declare Catalonia independent following a banned secession referendum.
Several hundred thousand Catalans rallied on Tuesday in fury at police violence against voters during a banned independence referendum, as Madrid accused regional authorities of "inciting rebellion".
The Mayor of the regional capital Barcelona Ada Colau issued a statement demanding "an immediate end to police charges against the defenceless population".
Thousands of people took to the streets of Barcelona on Wednesday as Spanish police detained 13 Catalan government officials in a crackdown ahead of an independence referendum deemed illegal by Madrid.