MILAN -- Italy's populist, anti-migrant interior minister said Friday that Malta should allow a Dutch-flagged rescue ship carrying hundreds of migrants rescued from rubber dinghies off the Libyan coast to make port there because the ship is now in Maltese waters. "We ask humanly and politically that Malta finally opens one of its ports and lets these desperate people disembark," and then seize the ship, Salvini said.

Malta responded that it would "act according to the laws and applicable conventions," without further explanation. International law states that Malta must respond if they are the nearest safe port at rescue or if requested by the ship's captain.

The dynamic is similar to the standoff over the Aquarius, operated by French aid groups, which eventually sailed an additional 900 miles last week to deliver 630 migrants to Spain after both Malta and Italy refused to let the rescue ship access their ports. Salvini is making good on an election promise to go after rescue ships run by aid groups, which he has likened to taxi services that help the migrant smugglers.

Salvini on Thursday said he would not allow the ship operated by the German NGO Mission Lifeline to enter Italian ports, saying that it had acted improperly by taking on board the 224 migrants that the Italian coast guard had assigned to the Libyan coast guard to rescue. Salvini said the rescue was in Libyan waters, which Lifeline denies.

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Mission Lifeline said Friday that it still has not been assigned a port, despite its requests. It said it picked up additional migrant passengers during another rescue overnight, and currently was heading north with 234 on board. It said it had responded to a request for help by a merchant vessel to help rescue 113 people.

Lifeline referred to reports that as many as 220 people were missing at sea and presumed drowned, according to survivor statements to the U.N. Refugee agency.

"The latest drownings show how important our sea rescue efforts are, and that not a single rescue ship can be missed," said Mission Lifeline founder Axel Steier. "The rescue of human lives must be prioritized before border control."

More than 640,000 migrants have arrived in Italy since 2014, many of whom made their way northward to join family or to countries perceived as providing more assistance until Italy's neighbors enacted stricter border controls. Arrivals are down some 80 percent this year to around 14,500, as migrants have turned to other routes.

How to handle the hundreds of thousands of migrants and refugees who have poured into Europe in recent years continues to be "one of the biggest crises that the European Union has faced in a decade where there have been several crises in a row," John Springford, Deputy Director of the Centre for European Reform, told CBS News this week.

The EU is a borderless travel zone, meaning once someone enters, he or she is able to move between EU countries freely. This "freedom of movement" allows citizens of EU member states to live and work in any EU country they please, but it also means once migrants cross over the bloc's external border, they are relatively free to move anywhere within the Eurozone.