Spain has issued an arrest warrant for former Catalan president Carles Puigdemont and four councillors, who are in Brussels.
A Madrid High Court judge issued the arrest warrant, asking Belgium to arrest Mr Puigdemont and the other four for extradition to Spain.
They face charges of rebellion, sedition and misuse of public funds, disobedience and breach of trust for their campaign for an independent Catalonia.
Mr Puigdemont and his associates ignored a court order to return to Spain to answer these charges on Thursday.
Mr Puigdemont has said he does not trust Spain for a fair trial, but has said he will comply with the Belgian courts.
“We are here because Brussels is the capital of Europe. This is a European issue and I want Europe to react,” said Mr Puigdemont.
He requested the opportunity to testify via video conference from Belgium, but this idea was rejected by the Spanish judge.
Nine members of Catalonia’s sacked cabinet are now in custody pending an investigation and potential trial.
The secessionist campaign has gained some momentum from the arrests, which have acted to galvanise supporters.
Pro-independence supporters staged protests that attracted thousands across several Catalan towns on Thursday night.
The Spanish government has conceded that it is willing to enter talks with the winners of the upcoming Catalan elections if pro-secessionist parties win.
“We could offer a new dialogue so that we can fulfil Catalans’ aspirations for more autonomy and look into reforming the constitution,” Foreign Affairs Minister Alfonso Dastis was quoted as saying in French newspaper Le Figaro.
“Some even mention the idea of a federal model so that regions can have more autonomy, including financially.”
The crisis arose after the Puigdemont government declared Catalonia an independent state following a referendum on the matter.
The Spanish government declared the referendum illegal and following the declaration, sacked the Catalonian government.