A private rescue ship carrying 629 migrants remained on a northward course in the Mediterranean Sea after more than a day of not receiving permission to dock in either Italy or Malta.
Aid group SOS Mediterranee said the passengers on its ship, the Aquarius, included 400 people who were picked up by the Italian navy, the country's coastguard and private cargo ships and transferred.
The rescue ship's crew pulled 229 migrants from the water or from traffickers' unseaworthy boats on Saturday night, including 123 unaccompanied minors and seven pregnant women.
The Aquarius and its passengers were caught up in a crackdown swiftly implemented by the right-wing partner in Italy's new populist government, which has vowed to stop the country from becoming the "refugee camp of Europe".
"Starting today, Italy, too, begins to say NO to the trafficking of human beings, NO to the business of clandestine immigration," Interior Minister Matteo Salvini, leader of the anti-migrant League party, tweeted on Sunday.
Mr Salvini and Transportation Minister Danilo Toninelli, who is part of the 5-Star Movement faction in the new government, said in a joint statement that it was Malta's responsibility to "open its ports for the hundreds of the rescued on the NGO ship Aquarius".
"The island can't continue to turn the other way," the ministers said. "The Mediterranean is the sea of all the countries that face it, and it (Malta) can't imagine that Italy will continue to face this giant phenomenon in solitude."
The Maltese government, however, was not moved. It said in a statement that the Aquarius took on the passengers in waters controlled by Libya and where Italian authorities in Rome coordinate search-and-rescue operations.
The Maltese Rescue Coordination Centre "is neither the competent nor the coordinating authority," the statement said.
SOS Mediterranee spokeswoman Mathilde Auvillain said the ship was "heading north following instructions received after the rescues and transfers" on Saturday night. The Rome-based rescue coordination centre gave the instructions.
Italy and Malta are blocking a migrant ship carrying 629 African migrants.June 10, 2018
The aid group said in a statement it had taken "good note" of Mr Salvini's stance, as reported earlier by Italian media. It added that the Aquarius "is still waiting for definitive instructions regarding the port of safety".
SOS Mediterranee said Maltese search-and-rescue authorities were contacted by their Italian counterparts "to find the best solution for the well-being and safety" of the people on the ship.
Farther west in the Mediterranean, Spain's maritime rescue service saved 334 migrants and recovered four bodies from boats it intercepted trying to reach Europe over the weekend. The rescue service said its patrol craft reached nine different boats carrying migrants that had left from Africa on Saturday and early Sunday.
One boat found on Sunday was carrying four bodies along with 49 migrants.
To the east, Libya's coastguard intercepted 152 migrants, including women and children, from two boats stopped in the Mediterranean off the coast of the western Zuwara district on Saturday. The migrants were taken to a naval base in Tripoli.
Human rights groups oppose returning rescued migrants to Libya, where many are held in inhumane conditions, poorly fed and often forced to do slave labour.
The United Nations says at least 785 migrants have died crossing the sea so far this year.