European Union authorities have hit back at a threat by Italy’s populist government to stop budget payments to Brussels, amid a deepening row over refugees and migrants stuck on rescue ship.

The Italian deputy prime minister has threatened to suspend his country’s financial contribution to the EU if Brussels does not intervene and redistribute the 150 refugees and migrants onboard a coastguard ship.

Luigi Di Maio, the leader of the Five Star Movement (M5S) which governs in coalition with the far-right League, said that if the EU did not act immediately his party would not be willing to give €20bn each year to the bloc.

The European commission said threats were unhelpful and called on all countries to find a solution to help the people onboard the Ulbaldo Diciotti, who have been denied permission to disembark from the Italian port of Catania by Matteo Salvini, Italy’s interior minister and League leader.

“Let’s not engage in finger pointing,” said a commission spokesman, Alexander Winterstein, when asked about the comments. “Unconstructive comments, let alone threats are not helpful, and they will not get us any closer to a solution. The European Union is a community of rules and it operates on the basis of rules, not threats. So we would call on all parties involved to find a swift solution for the persons on board in the spirit of good cooperation.”

The 150 people onboard the coastguard ship have gone on hunger strike, having been prevented from disembarking since Monday.

On Thursday, Di Mario said: “We have had enough, Europe must strike a blow. If tomorrow they do not make a decision about the Diciotti and the redistribution of migrants, M5S and I will suspend the funding.”

The EU budget pays for common policies, such as farm payments, infrastructure projects and running the EU. Member states pay their membership dues monthly, giving Di Maio an imminent opportunity to flex his political muscles. But Italy would jeopardise the payments it receives, which totalled €10bn in 2017 and almost €12bn in 2016, if it makes good on its threat. The country was granted a further €9m in recent days to help it cope with the numbers of refugees and migrants crossing the Mediterranean.

The commission, which is the guardian of EU law and can take recalcitrant governments to the European court of justice, declined to comment on the consequences if the Italian government refused to pay its dues.

The sharp exchange highlighted the stalemate over which country will help the people onboard the Dicotti. Senior officials from 12 member states were holding emergency talks in Brussels on Friday. The commission said the meeting was not organised to find an immediate solution, but to find a long-term answer to the migration crisis.

“What we are looking for is a structural, sustainable solution, moving away from this ship-by ship troubleshooting,” said Winterstein.

EU leaders agreed in testy, all-night talks in June to create special “controlled centres” to process the asylum claims of people rescued from the Mediterranean. But the agreement appears merely to have papered over divisions and no country has agreed to set up a centre on its soil.

Salvini risks coming under investigation after the prosecutor of Agrigento, Sicily, opened an inquiry into the illegal detention of passengers, due to the interior minister’s refusal to allow them to disembark.

The Diciotti rescued 190 people from an overcrowded boat about 19.5 miles from the Italian island of Lampedusa on 15 August. Thirteen of them were evacuated for emergency medical treatment.

Rome insisted that Malta should take the group because the boat first passed through the country’s search-and-rescue area, but Valletta refused, claiming the people wanted to reach Italy.

On Monday afternoon, Italy’s transport minister, Danilo Toninelli, tweeted: “The Diciotti ship will dock in Catania.”

But shortly afterwards Salvini’s press officer said the interior minister had not given, and would not give the authorisation for the 177 refugees and migrants to disembark until he was assured that all would “go elsewhere”.

On Wednesday afternoon, prosecutors in Agrigento visited the ship and questioned the captain and several of its passengers.

The investigation was launched against “unknowns”. But Salvini could end up under investigation if magistrates go ahead with judicial proceedings because he ordered the disembarkation ban.

“I heard that the prosecutor’s office in Agrigento has opened an investigation,” he said in a video on Facebook Live. “I also heard that the suspects are ‘unknown’ at the moment. But I’m not unknown. My name is Matteo Salvini, I’m the minister of the interior. Come on, try me too, I’m here.”

Salvini authorised on Wednesday night for the 27 unaccompanied minors to disembark after he was visited by magistrates, but made clear he would not allow the remaining 150 onboard to also do so unless “Europe stepped in”.

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