Matteo Salvini, Italy’s far-right interior minister, has asked his government to deny prosecutors the right to try him on potential kidnapping charges over his order to prevent 177 people from disembarking a migrant boat.

The move is a stark reversal from Salvini’s previous position that he was ready to be tried and proud of “having defended the country from illegal migrants”.

In August, prosecutors in Agrigento, Sicily, placed Salvini under investigation after he prevented people from leaving the Italian coastguard ship Ubaldo Diciotti. The ship had been docked for six days at the Sicilian port of Catania as Salvini maintained a standoff with the EU in an attempt to push other member states to take in its mostly Eritrean passengers. The Catholic church, Ireland and Albania, which is not an EU state, eventually agreed to host the migrants.

But the breakthrough did not stop the investigation into Salvini and the minister is a step away from facing court after a surprise ruling last week determined that he be tried. “I could face up to 15 years of jail because I have stopped the disembarking of illegals in Italy,” Salvini wrote on Facebook. “I’m speechless. Am I afraid? Not at all.”

Nevertheless, in a letter to the Italian newspaper Corriere della Sera published on Tuesday, Salvini, the leader of the far-right League party, said he was no longer sure he was ready to face a trial.

“After reflecting on the whole affair, I believe the authorisation to try me must be denied,” he wrote. “My judicial case is closely linked to my activities as interior minister and my strong will to keep the commitments made in the election campaign. I’m convinced that I acted in the supreme interest of the country and within the full respect of my mandate.

“I would do it all again. And I won’t give up,” he wrote, but added: “The judges should be denied authorisation.”

The investigation of Salvini poses a political risk to Italy’s governing coalition as well as a personal risk to his criminal record.

The accusations against him will pass now through the senate, whose members will decide whether to proceed with a trial or halt the proceedings altogether. One of the founding principles of the League’s coalition partner, the Five Star Movement (M5S), is that politicians under investigation should be asked to resign.

Until two years ago, this principle was written into M5S’s statutes as part of an attempt to present a clean image and distance itself from corruption in Italian politics. On one hand, should M5S senators vote against criminal proceedings, thereby rescuing Salvini from a possible conviction, the party would lose credibility among its supporters. On the other, if it supports the investigation against Salvini, then it risks losing him and the political alliance, causing the government to fall.

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M5S had seemed willing to vote in favour of authorising a trial but after the publication of Salvini’s letter, Luigi Di Maio, the M5S deputy prime minister, filed a document with the prime minister, Giuseppe Conte, formally defending him. “If Salvini is responsible for the [migrant boat] seizure then the whole government is responsible,” the document said.

A senate commission will meet to begin examining the papers on the investigation into Salvini on Wednesday. The vote on whether to proceed is expected in late February.

Conte said on Wednesday that 47 people kept at sea for over a week on the Sea-Watch 3 migrant rescue ship could finally disembark after six countries came forward to take them in.

The people were rescued on 19 January off the coast of Libya and have been waiting off Sicily since Friday. As in the Ubaldo Diciotti case, Salvini denied Sea-Watch 3 the right to dock, drawing the ire of the UN and prompting an emergency appeal to the European court of human rights by the German NGO that operates the boat.