Italy will refuse to let a humanitarian ship carrying more than 600 migrants dock at its ports and has asked the Mediterranean island of Malta to open its doors to the vessel, government officials said on Sunday.

Malta brushed off the request, saying it had nothing to do with the rescue operation, opening the prospect of a diplomatic rift between the two European Union allies.

The move by Italy's new interior minister, Matteo Salvini, who is also head of the far-right League, represents an opening gambit to make good on his electoral promises to halt the flow of migrants into the country.