European far-right leaders have rallied to the side of Italian Deputy Prime Minister Matteo Salvini, who faces a possible six-year jail term for refusing to let a migrant boat dock when he was interior minister in 2019.

Hungary's Viktor Orban and Dutch nationalist Geert Wilders joined senior politicians from across the continent to address the annual rally of Salvini's League party in the northern Italian village of Pontida.

"You are our hero. We stand with you. That's why we are here," said Wilders, whose anti-Islam party joined the government in the Netherlands for the first time this year - an indication of the growing power of the far-right in Europe.

A number of like-minded parties joined forces at a European level in June, creating the Patriots for Europe group - the third biggest bloc in the EU parliament, which is looking to curb the power of Brussels and halt unauthorized immigration.

Salvini burnished his standing as an anti-immigrant firebrand last month when a prosecutor demanded he be handed a six-year prison term over his 2019 decision to prevent more than 100 migrants from landing in the country.

Prosecutors say he effectively kidnapped the migrants, forcing them to stay at sea for almost a week, despite increasingly bleak conditions on their boat.

"He deserves exultation, not punishment," Orban told the crowd of flag-waving League supporters. "He defended the homes of Italians, and he has also defended Europe."

The next hearing in the migrant case is on October 18, but it is not clear when a verdict will be handed down.

"They can arrest a single person who defended national borders, but not a whole people. They cannot stop this holy alliance of European peoples that is born today in Pontida," Salvini said, adding that he hoped Donald Trump would be elected president at next month's U.S. election.

Orban said anti-immigrant sentiment was spreading across Europe and threatened to take asylum seekers to Brussels unless the European Court of Justice rescinded a daily €1 million ($1.1 million) fine on Hungary for breaking asylum laws.

"If they continue to punish us, we will transport migrants from Budapest to Brussels," he said. "If they want the migrants, they can keep them."

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