And the crisis between the Mediterranean countries may be far from being over, as Italian newspaper Repubblica reported that 800 more people have been saved by both Italian and worldwide boats in Libyan waters overnight.
Malta's government replied to the statement saying Prime Minister Joseph Muscat had spoken to Italian premier Giuseppe Conte, and underlined "that Malta is acting in full conformity with its worldwide obligations".
A humanitarian ship with more than 600 migrants on board remains adrift in global waters as Italy and Malta are at loggerheads over which country should take them.
He tweeted: #Chiudiamoiporti. "We're closing the ports". Salvini campaigned on an anti-immigrant platform that also included a vow to expel hundreds of thousands of migrants already in Italy, even though experts doubt such mass deportations are feasible or financially viable.
Salvini pointed to Malta's unwillingness in accusing Europe as a whole of leaving Italy on its own to deal with the refugee crisis.
The Aquarius ship, run by the NGO SOS Méditerranée, was en route to Sicily with 628 people on board but was left stranded yesterday after Italy shut its ports and demanded Malta take it instead.
Italy's new interior minister Matteo Salvini has called on Malta to open its border.
According to the daily Corriere Della Sera, the letter describes Malta's capital, Valletta, as the "most secure port" and the boat should thus dock there.
Italy's former ambassador to Malta has urged the two countries to tone down their rhetoric and seek a common solution to the fate of the Aquarius migrant ship.
Transport Minister Danilo Toninelli, who is nominally in charge of the ports, said: "Malta can not continue looking the other way when it comes to respecting global conventions". In practical terms, no ships of this type will be able to land without cooperation of the Italian coastguard, which is under the direct command of the Italian government. "RCC Malta in this case is neither the competent, nor the coordinating authority".
SOS Mediterranee said late Sunday that it had received instructions from Italian authorities to hold position between Malta and Italy after previously heading north.
The group said it "urgently requests a swift resolution and a designated port of safety".
Charity boats operating off the Libyan coast have played an increasingly important role in rescuing migrants, who often put to sea in flimsy inflatable boats not designed for the open ocean.
For years the European Union has largely ignored Italy's rising fury at being left to deal with the migration crisis (even when it came from more politically acceptable figures like Matteo Renzi) but with Mr Salvini in charge, that may no longer be possible.
The charity say they have enough supplies to feed the migrants at least for another day.