Founded in 1980, the neofascist party Golden Dawn came to international attention in 2012 when it entered the Greek Parliament for the first time, winning 18 seats . The election results came amid the country’s debilitating debt crisis and resulting austerity measures.

The party, which the Council of Europe’s human rights commissioner described in 2013 as “neo-Nazi and violent,” holds extreme anti-immigrant views, favors a defense agreement with Russia and said the euro “turned out to be our destruction.”

In September 2013, the Greek authorities arrested dozens of senior Golden Dawn officials, including members of Parliament and the party’s leader, Nikos Michaloliakos, who was charged with forming a criminal organization.

Golden Dawn, which again won 18 seats in parliamentary elections in September, was largely silent as the migrant crisis in Greece began, but in recent weeks, members have been marching in several areas where migrants are camped .

Party leaders, since released from custody as their trial continues, have said Golden Dawn is planning numerous protests around the country against what they warn is the “Islamization of Greece.”

The National Front is a nationalist party that uses populist rhetoric to promote its anti-immigration and anti-European Union positions.

The party favors protectionist economic policies and would clamp down on government benefits for immigrants, including health care, and drastically reduce the number of immigrants allowed into France.

The party was established in 1972; its founders and sympathizers included former Nazi collaborators and members of the wartime collaborationist Vichy regime. The National Front is now led by Marine Le Pen, who took over from her father, Jean-Marie Le Pen, in 2011.

She has tried to soften the party’s image. Mr. Le Pen had used overtly anti-Semitic and racist language and faced repeated prosecution on accusations of Holocaust denial and inciting racial hatred.

In the first round of voting in regional elections in December, the National Front won a plurality of the national vote (27 percent), but in the second-round runoffs, the party was denied victory in all 13 regions.