Spain's Supreme Court suggested that the two high-ranking Catalan separatists were likely to continue their illegal activity if they were to be released.
The former leader of the Catalonia government, Carles Puigdemont, and four of his disbanded cabinet, are in self-imposed exile in Belgium under conditional release after an worldwide arrest warrant was served against them.
On Monday six other ministers were released from prison near Madrid on bail.
After their failed independence bid, which saw leaders being detained or fleeing overseas, Catalan separatists head into a new election this month divided over the future of their region but united against what they say is "repression" from Madrid.
Its candidates are running on separate lists to Puigdemont's as the two parties compete for hegemony of the separatist bloc.
"They could open up a rift that prevents them returning an overall majority".
Voters are choosing regional lawmakers and top government officials to replace the pro-independence officials removed by the national government in late October.
His former deputy Oriol Junqueras, one of those detained following the independence declaration, and who could be released on bail as early as Monday, hopes to see his ERC party, which is leading polls, to victory on December 21.
The magistrate also upheld custody orders without bail for the former regional interior minister, Joaquim Forn, and the leaders of Assemblea Nacional Catalan and Omnium Cultural, the two Catalan grassroots groups that have been the main drivers of the separatist bid in Catalonia.
Germany meets Mexico and Portugal will get Spain
The ceremony was staged inside the State Kremlin Palace, where Communist Party Congresses were held during the Soviet era. Further afield, in Kazan and Kaliningrad, Spain will play their remaining group games.
A government-run poll published Monday indicated that pro-independence parties would lose their slim majority in Catalonia's parliament. All Catalan politicians have faced charges of rebellion and sedition.
A judge decides Monday if jailed Catalan pro-independence politicians and activists should be released, paving the way for them to join campaigning in a polarized regional election this month.
Yesterday, Paul Bekaert, Puigdemont's defence lawyer, argued that the Spanish charges, which carry punishments of decades in prison, are not punishable in Belgium, and so grounds for extradition do not apply.
Mr Junqueras and the other jailed politicians pledged last week to give up on efforts to seek unilateral independence for the wealthy northeastern region, in the hope of being freed.
The Dec. 21 ballot is shaping up as a plebiscite between those for and against independence.
Despite his self-imposed exile, Puigdemont is heading his party's campaign for the December 21 election.
The unexpected decision comes just a day after Puigdemont and his four former ministers attended an extradition hearing in Brussels.
The prosecution, as well as those being prosecuted, have the right to appeal the final decision.