Authorities in Madrid and Barcelona locked horns over whether two jailed Catalan pro-independence leaders were political prisoners, as their detention looked set to reignite secessionist protests.

The Madrid High Court upped the stakes on Monday in Spain's worst political crisis in decades, moving to thwart Catalonia's independence push by jailing the heads of its two main separatist groups pending an investigation for alleged sedition.

Catalan leader Carles Puigdemont, given a Thursday deadline to renounce independence or face the threat of direct rule from Madrid, tweeted following the detentions: "Sadly, we have political prisoners again."