Catalonia's regional government is mulling when to declare the region's independence from Spain in the wake of a disputed referendum that has triggered Spain's most serious national crisis in decades. Some lawmakers say that will happen Monday.

The region's pro-independence president, Carles Puigdemont, who has said an independence declaration will come in a few days, is delivering a speech later Wednesday. He's also addressing the regional parliament on Monday to review the vote — a session that his parliamentary supporters in the radical, anti-capitalist CUP group say will consider the independence declaration.

Spain, which has declared Sunday's referendum illegal and invalid, is bitterly opposed to any independence move.

Spain's conservative government has said it will respond with "all necessary measures" to counter Catalan defiance, and is holding talks with opposition leaders in Madrid to forge a consensus over what to do in response.

It's anybody's guess what might happen if the prosperous northeastern region of Catalonia does actually try to secede. Spain could intervene to take over the regional government or it could even declare a state of emergency and impose martial law.

In a nationally televised address Tuesday night, Spain's King Felipe VI came out strongly against the actions of Catalan authorities, saying they had deliberately bent the law with "irresponsible conduct."

The Spanish state, he went on, needed to ensure constitutional order and the rule of law in Catalonia, which is the richest region of Spain.

Catalonia says some 2.3 million people — less than half the region's electorate — voted in the referendum Sunday. Many of those opposed to independence are thought to have stayed at home after the referendum was ordered suspended by a Spanish court. Of those who voted, some 90 percent backed independence, according to Catalan officials.

Xavier Garcia Albiol, the top politician in Catalonia of Spain's governing party, called Wednesday for Catalans who want to stay inside Spain to join a rally Sunday in Barcelona that has been organized by the pro-union grassroots Civil Catalan Society group.

The route to becoming independent won't be easy for Catalonia. The region doesn't have any power over defense, foreign affairs, taxes, ports or airports, all of which are in the hands of the Madrid government. The European Union has also said that an independent Catalonia cannot stay in the bloc, but must apply to join, a lengthy uncertain process.

The crisis in Spain grew more acute Sunday when some 900 people needed medical attention after police cracked down to try to prevent the vote. Over 400 police also had bruises.

On Tuesday, huge crowds held street protests and unions staged a strike in Catalonia to protest the alleged police brutality.

Spain's National Court on Wednesday said it will quiz two senior officers of Catalonia's regional police force and the leaders of two pro-Catalan independence civic groups who have been placed under investigation for sedition.

The court said the four will be questioned Friday about their roles in demonstrations Sept. 20-21 in Barcelona, when Spanish police arrested several Catalan government officials and raided offices in a crackdown on preparations for the referendum.

Spanish authorities say the demonstrations hindered the police operation. During the rallies, there were some disturbances.

The four include regional police chief officer Josep Lluis Trapero and Jordi Sanchez, the head of the Catalan National Assembly that has been the main civic group behind the independence movement.