Madrid (AFP) - Catalonia's government has threatened to declare independence after the region voted in an outlawed referendum.

Here are six key players in Spain's deepest political crisis in decades:

- Mariano Rajoy -

The 62-year-old leader of the conservative Popular Party (PP) has served as Spain's prime minister since December 2011.

Rajoy has headed a minority government since a 2016 general election, backed by centrist party Ciudadanos.

His detractors accuse him of not having done anything to stop separatist sentiment from surging in Catalonia.

Rajoy argues he could not negotiate an independence referendum in the region because it violates Spain's constitution which declares the country indivisible.

He has refused to rule out an unprecedented constitutional manoeuvre to impose direct rule on the region from Madrid -- a move that could spark unrest.

- Carles Puigdemont -

The 54-year-old president of Catalonia, a former journalist, has advocated for independence since his youth.

He became head of the regional government at the start of 2016.

It is believed he may declare Catalan independence on Tuesday after 90 percent of voters who took part in the referendum backed breaking away from Spain, out of a turnout of 43 percent.

Puigdemont has said he is willing to go to jail over his separatist push.

He is under investigation for alleged crimes of civil disobedience, abuse of office and misuse of public funds for staging the plebiscite.

- Soraya Saenz de Santamaria -

Spain's deputy prime minister, 46, is in charge of the central government's relationship with its regions.

She launched an "operation dialogue" with Catalonia's separatist government but failed to convince them to drop their plans to hold an independence referendum.

Spain's central government in March promised to invest 4.2 billion euros ($4.9 billion) in Catalonia, mostly in rail infrastructure, between 2017 and 2020.

That was considered by many to be too little, too late in a region which has long demanded more powers and money for infrastructure.

- Oriol Junqueras -

Junqueras is the 48-year-old is the leader of the leftist Esquerra Republicana de Catalunya (ERC) party, which has called for Catalan independence since 1931.

A lawmaker in the European Union parliament from 2009 to 2011, since January 2016 he has been the vice president of Catalonia.

Like Puigdemont, this history professor at the University of Barcelona is also being investigated for civil disobedience, abuse of office and misuse of public funds over the referendum.

- Carme Forcadell -

The president of the Catalan regional parliament since October 2015, Forcadell has for years helped organise massive street demonstrations for Catalan independence. She belongs to the ERC party.

She was fiercely criticised in early September for pushing through two laws that paved the way for the referendum through the assembly with little debate.

The laws were swiftly suspended by Spain's Constitutional Court.

She is also being investigated for civil disobedience, abuse of office and misuse of public funds.

- Ada Colau -

The 43-year-old former social activist was elected mayor of Barcelona, the capital of Catalonia, in 2015.

She became well known as the spokeswoman of a group that fought housing evictions at the height of Spain's economic crisis.

Colau says she has never been pro-independence but she defends Catalonia's right to hold a secession referendum with the agreement of Spain's central government.

On Monday she urged Puigdemont not to declare independence, warning that it would put "social cohesion" at risk.