Thousands of Catalan separatist supporters marched in Madrid on Saturday in protest over the ongoing trial of 12 separatist leaders who face up to 25-year-prison sentences for their role in the failed independence bid.

The demonstration through Spain's capital was organised by two civil society groups the Catalan National Assembly (ANC) and Òmnium Cultural and led by Catalan leader Quim Torra.

Demonstrators waved the Catalan flag and marched under signs reading: “Self-determination is not a crime”.

Protest organisers said 120,000 attended the protest while police said there was a turnout of 18,000.

Twelve Catalan separatist leaders are currently on trial in Madrid over a range of allegations including rebellion and misuse of public funds for the failed independence bid in October 2017, which they deny.

The Catalan crisis is set to be monumental in the upcoming general election in April. Three right-leaning parties, the conservative People’s Party (PP), center-right Ciudadanos, and far-right Vox party have called on the government to take a tougher stance with separatists.

Socialist Prime Minister Pedro Sanchez is also likely to need support from the Catalan parties as polls predict his PSOE party will win most seats but still fall short of a parliamentary majority.

Sanchez called the snap vote after he failed to get enough support for his draft budget. Back then, he was reliant on the Catalan pro-independent parties support for it to pass but they voted against it.