Ex-Catalonia chief Carles Puigdemont has hit out at the European Union for being "more concerned" about Venezuela than what is happening in Madrid.

Puigdemont, in self-imposed exile, was speaking in Berlin as a dozen Catalan leaders went on trial in Madrid charged over the 2017 failed bid to split from Spain.

He said Brussels defended human rights around the world but not on its own doorstep regarding Catalan separatists.

"Why is the European Union more concerned with what is happening in Venezuela than what is happening in Madrid today?" he asked.

Puigdemont said the trial was a stress test for Spain's judiciary and democracy.

"Be confident and look to our social and political leaders," he said, asked how those in favour of independence should react today. "They are very strong and are defending for us values that we want to decide our own future."

READ MORE: Euronews explains Catalan separatists' trial and what it could mean

The defendants who went on trial on Tuesday are facing charges of rebellion, sedition and misuse of public funds for their role in the north-east region's failed independence declaration.

Puigdemont, the former president of Catalonia, is the big absence from the trial. He fled to Belgium on October 30, 2017.

"The fact is the support for the pro-independence parties was higher than the support for parties explicitly against independence," said Puigdemont, pointing to the most recent elections in the region to support his desire for secession from Madrid.

Puigdemont, though, saved his strongest words for the Spanish government when asked why he wasn't at home facing justice.

"I want to return to my home, I want to return to my family," he said. "But I want to return to a real democracy with a clear separation of powers and that is not possible in Spain."

Today's trial is linked to the attempt to Catalonia's attempt to declare independence from Madrid in October 2017.

Voters backed splitting from Spain in a banned referendum.

Madrid responded by imposing direct rule, sacked the parliament in Catalonia and called fresh elections, which nationalists won.

Secessionists have called on Catalans to briefly stop work at midday on Tuesday in protest against the trial and to join a rally in Barcelona in the evening.

The political right organised a mass protest on Sunday in Madrid against any concessions by Socialist Prime Minister Pedro Sanchez to Catalan pro-independence parties.

The trial starts as Sanchez's minority government faces a vote on the 2019 budget on Wednesday for which it needs the support of Catalan parties. They have so far vowed to block the bill, citing Sanchez's refusal to discuss independence, despite his efforts to ease tensions with the Catalans through talks.

Failure to approve the budget is likely to prompt a snap parliamentary election this year.