ROME — The leaders of the populist parties that formed Italy’s government sparred Saturday over more migrants stranded on private rescue vessels in the Mediterranean Sea, exposing cracks in their coalition’s position on immigration.

German humanitarian groups Sea-Watch and Sea Eye are seeking a port where two ships can disembark passengers who were picked up from unseaworthy smugglers’ boats, 32 of them on Dec. 22, and 17 more in recent days.

Malta allowed the aid boats to shelter from bad weather near its coast and to take on fresh crew, food and water. But the tiny island nation has refused to let any of those migrants step onto Maltese land, saying the rescues took place outside the country’s search-and-rescue area.

Italian Deputy Premier Luigi Di Maio, who heads the 5-Star Movement, insisted Saturday that Malta had to allow the 49 people off the ships. De Maio said Italy was willing to take the 10 mothers on the aid vessels and their children.

Since the coalition government came to power in mid-2018, Interior Minister Matteo Salvini, who heads the anti-migrant League party, has made it strict policy that no private aid group receive authorization to transfer rescued migrants to land in Italian ports.

Both he and Di Maio have likened private aid vessels to “taxi services” for Libya-based human traffickers. Amid criticism of the Italian government’s new hard-line stand, they also have reminded other European Union nation’s that Italy has taken in hundreds of thousands of rescued migrants as asylum-seekers in recent years.

Di Maio stressed Saturday that Italy was offering to accept the limited number of women and children from the rescue ships to keep families together. Such as gesture, he said, would also give “a good moral slap” to EU nations that have ignored Italy’s insistence that the burden of caring for rescued asylum-seekers be shared.