Libya is a key departure point for thousands of migrants hoping to reach Europe, although hundreds drown each year attempting the crossing.
Salvini's unexpected trip came a day after emergency talks between 16 European Union leaders in a bid to break a longstanding deadlock over who should take in the migrants, the bulk of which have been landing in Italy and Greece.
The crisis came to a head earlier this month when Italy's new populist government turned away a rescue boat carrying 630 people, which was also rejected by Malta, forcing the vessel to remain at sea until Spain offered them safe haven.
But the relief was short-lived, with Italy and Malta refused a second vessel carrying 234 migrants who were rescued on Thursday. The move left Germany-operated rescue boat Lifeline stranded in international waters near Malta.
"Let's see if Europe remembers that it actually exists because there is still a boat loaded with migrants in Maltese waters waiting for a port to welcome it and we can tell you again, it won't be in an Italian port," Salvini said.
A Danish cargo ship owned by Maersk, the world's leading container shipping company, has also been stuck off Sicily since Saturday with 108 migrants on board, awaiting instructions from the Italian authorities.
Ramping up the rhetoric, Salvini earlier issued a blunt rebuke, warning foreign charities to stop rescuing migrants off Libya, accusing them of "causing trouble" and saying Italian ports "are and will be closed to those who aid human traffickers." His remarks came as Libya's coastguard said it had rescued nearly a 1,000 people on Sunday, and Spanish authorities said they had picked up more than 600 others off their coast.
Salvini has insisted Italy will not take in "one more" refugee, vowing to close its ports to all foreign-flagged rescue ships and demanding that Europe shoulder the burden, warning the migration crisis could threaten the bloc's future.
"We will jointly support, with Libyan authorities, the setting up of reception and identification centres south of Libya, on the external border of Libya, to help Libya as well as Italy block migration," Salvini told a news conference in Tripoli.
Ahmed Maiteeq, deputy head of the Government of National Accord (GNA), said Libya would host a migration summit in September. Earlier, he told Italy's La Repubblica that Europe "must think of structural measures to take in African countries to stop migrants." On his return to Rome, Salvini said a technical team would be set up this week with representatives from Italy, Niger, Chad and Mali.
He dismissed calls by France and Spain for asylum-seekers to be kept in closed centres until their claims are processed -- a proposal Rome fears would turn Italy into "a refugee camp for all of Europe". "Welcome hotspots in Italy? It would be a problem for us and for Libya itself because it would not stop these deadly waves (of migration). We have proposed reception centres south of Libya to avoid Tripoli becoming a funnel, like Italy," he wrote on Twitter.
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