The former Catalan president Carles Puigdemont and two of his former ministers are to be excluded from standing in next month’s European elections after Spain’s central electoral board upheld an appeal from two rightwing parties.

Puigdemont, who fled Spain to avoid arrest after his regional government’s unilateral independence referendum in October 2017, intended to run as a candidate in the European parliament elections for the Together for Catalonia platform.

Also on the list are former Catalan education minister Clara Ponsatí, and Toni Comín, who was health minister in Puigdemont’s administration.

But it emerged on Monday that the electoral board had accepted a petition from the conservative People’s party and centre-right Citizens party that the trio’s candidacies be declared ineligible because all three are “fugitives” abroad.

Puigdemont and Comín are in Belgium, while Ponsatí is in Scotland. They face arrest in Spain for their alleged roles in the referendum and subsequent unilateral declaration of independence.

A spokesman for Puigdemont said an appeal would be launched.

“Together for Catalonia – Free for Europe intends to respond to this brazen violation of their fundamental right to stand as candidates by taking any necessary legal actions in Spain and Europe to defend the rights of all three candidates and the right of voters to cast their vote for this republican list,” he said.

“We will not simply accept a resolution that clearly breaks Spanish and European law and undermines a pillar of democracy, as so often happens in the Spanish legal system when pro-independence politicians are involved.”

Teodoro García Egea, the general secretary of the People’s party, said its actions had ensured “justice will not be brushed aside and a fugitive allowed to represent the Spanish people”.

A dozen pro-independence Catalan leaders are on trial at the supreme court in Madrid for their alleged roles in the push to secede, including the region’s former vice-president Oriol Junqueras.

Junqueras and four other defendants were elected to the Spanish congress and senate in Sunday’s general election.

The two main independence parties, the Catalan Republican Left and Together for Catalonia, won 22 of the region’s 48 seats in the poll, five more than they took in the last election in June 2016.