MADRID -- Catalonia's acting regional president has been placed under investigation by a court for his role in staging a referendum on independence last year, officials said Tuesday.

Artur Mas will appear Oct. 15 for questions concerning the Nov. 9, 2014, independence referendum called by him, Catalonia's regional justice department said. The plebiscite was held despite having been suspended by the constitutional Court.

On Sunday, Catalonia held a regional election and the "Together for Yes" pro-independence alliance headed by Mas won 62 seats in Catalonia's 135-member parliament -- six short of a majority. Mas had promised to go for secession if they had achieved a majority.

Catalonia labeled the 2014 referendum an informal process to try to skirt the suspension order. The constitutional Court later ruled the plebiscite to have been unconstitutional.

Catalan officials said that out of 6.3 million potential voters, 2.3 million cast ballots on the day, with most favouring secession.

Prosecutors accuse Mas of grave disobedience, abuse of public funds, prevarication, usurpation of powers and obstructing justice. If tried and found guilty, he could face a period of disqualification from office or up to one year in jail.

Two other associates are also under investigation.

Following the referendum, Mas set about using Sunday's regional parliament elections as a substitute vote on independence.

Besides not getting a seat majority, the "Together for Yes" alliance and the other main pro-secession party, CUP, only managed to get 48 per cent of the vote altogether against 52 per cent for parties opposed to independence.

Mas must now seek parliamentary support to form a government but CUP, a radical anti-capitalist group that won 10 seats, says it will back the alliance but won't help Mas become regional president.

Spain has ruled out any possibility of Catalonia becoming independent, saying it would be unconstitutional. It has pledged to use all powers available to block such a move.

The newly-elected Catalan deputies are to take their seats by Oct. 26 and elect a new regional president by Nov. 9.