A call by Italy for France and Spain to offer up their ports for the disembarkation of migrants rescued in the Mediterranean has failed to garner the backing of EU member states, despite Rome’s threat to pull the plug on the EU’s Operation Sophia rescue mission.

Hijacking a meeting of defence ministers in Vienna, the Italian representative, Elisabetta Trenta, called the ports where rescue ships dock to be rotated to lift the burden on her country.

Italy became the main route into Europe for hundreds of thousands of asylum seekers arriving by sea since the other main route from Turkey to Greece was largely shut in 2016. While numbers have dropped over the past year, the new populist Italian government has made shutting down the route a policy pillar.

The EU’s high representative for foreign affairs, Federica Mogherini, confirmed to reporters that Italy had tabled the proposal, but said the meeting was not the place for decisions on the issue to be made.

Mogherini said that, as it stood, Italy’s proposal neither had the required unanimous backing of the other member states nor could she be confident support would be found in the coming weeks.

She said Italy had agreed that the Mediterranean search and rescue mission must continue beyond its current term, which ends in December.

“Today ... it was for me and some ministers around the table, not least the Italian one, to check if there was a political will to guarantee the continuation of the operation and it is definitely the case,” she said. “To the question of, ‘Do we want and firmly want to continue Operation Sophia’, the answer was definitely: ‘Yes.’”

But this appeared to be at odds with the position of Italy’s interior minister and deputy prime minister, Matteo Salvini. He told reporters on Thursday: “We are preparing some proposals to Brussels as we did in the past. They always said no. If they continue saying no, we’ll deal with this [migration] on our own’’.

Salvini, whose far-right League party entered government in a coalition with the Five Star Movement this year, has taken a hard line on immigration, repeatedly saying Italy will “no longer be Europe’s refugee camp”. Attacks on immigrants in Italy have risen since the election.

About 650,000 people, mostly from Africa and the Middle East, have landed on Italian shores since 2014.

The Italian demand follows diplomatic rows in which rescue ships were not allowed to dock in Italy unless other states agreed to take in the people on board.

Salvini was placed under investigation last week by Italian prosecutors from Agrigento in Sicily for potential abuse of office, kidnapping and illegal detention, relating to his refusal to allow 177 migrants onboard the coastguard ship Ubaldo Diciotti to come onshore.

Salvini prevented the passengers from disembarking for almost a week while calling for guarantees that other EU member states would take their share. After his request was refused, Salvini said he would meet the Hungarian prime minster Viktor Orbán to discuss “alternative strategies”.

On Tuesday, following their meeting, Salvini and Orbán claimed they were “walking down the same path” after discussing the formation of a common anti-migration front to oppose the policies of the French president, Emmanuel Macron.

“We want to change Europe’s commission. We want to protect our borders. We are going to fight pro-migrant policies supported by Macron and [George] Soros,” Salvini said.

Macron responded on Thursday: “Salvini and Orbán are right to consider me a threat because we will not cede any ground to nationalists and those who advocate hate speech.”

Salvini in turn told reporters: “France sent back to Italy 48,000 migrants from its borders. He better shut up.”

Mogherini said there would be a review of the rules of Operation Sophia, but that it was vital to continue it under any circumstances given the risk of a return to large-scale deaths in the sea.