However, Mr Salvini does not have authority over the ports and it was not immediately clear if his line would hold.
Malta Prime Minister Joseph Muscat on Sunday evening told his Italian counterpart, Giuseppe Conte, Malta will not allow the ship to disembark.
Italy and Malta dug in for a second day Monday and refused to let a rescue ship with 629 people aboard dock in their ports, leaving the migrants at sea as a diplomatic standoff escalated under Italy's new anti-immigrant government.
Despite the claim by Mayor Orlando that the government stands in opposition to worldwide law by closing the ports to migrant smuggling operations, a distinguished expert on global maritime law Admiral Paolo Caffio has given his verdict, stating that not only is it legal, but there is also precedent, reports Il Giornale.
Earlier on Sunday, the charity SOS Mediterranee on Twitter that its rescue ship, The Aquarius, had taken on board 629 refugees and migrants, including 123 unaccompanied minors, 11 other children and seven pregnant women.
Mr Salvini says he wants to "stop the death boats".
Malta said the rescue operations took place in global waters off Libya and were coordinated by Italy. That stance "confirms the latest unwillingness of Malta and, thus, of Europe, to intervene and take care of the emergency".
There was no comment from the Italian Ministry of the Interior or the local coastguard.
The government of Malta expressed concern that Italy is going against worldwide rules in the way it is tackling the issue regarding stranded migrants.
"Malta is neither the competent nor the coordinating authority in this case".
Why has Italy closed its ports to the migrants?
SOS Mediterranee said the crew of the Aquarius were still at sea and awaiting instructions.
Sea-Watch said police also questioned some of the rescued migrants who, after being processed by the authorities, are likely to end up in reception centres.
Dalli accused the Italian government of breaching global maritime laws by refusing to allow the Aquarius to berth in its ports. We have always welcomed rescue boats and vessels who saved lives at sea.
To the east, Libya's coast guard intercepted 152 migrants, including women and children, from two boats stopped in the Mediterranean off the coast of the western Zuwara district Saturday.
Italy has had to deal with hundreds of thousands of migrants in recent years coming via Libya to reach Europe.
The UN refugee agency on Monday called on Italy and Malta to immediately allow a boat carrying hundreds of migrants to dock, describing the situation as "an urgent humanitarian imperative".
The United Nations estimates at least 500 people have died in 2018 trying to cross the central Mediterranean, following more than 2,800 fatalities past year.