A private rescue ship carrying 629 migrants remained at sea after more than a day of not receiving permission to dock in either Italy or the small Mediterranean island nation of Malta.
Aid group SOS Mediterraneee said the passengers on its ship, the Aquarius, included 400 people who were picked up by the Italian Navy, that country's coast guard and private cargo ships and transferred.
The rescue ship's crew itself pulled 229 migrants from the water or from traffickers' unseaworthy boats on Sunday, including 123 unaccompanied minors and seven pregnant women.
The Aquarius and its passengers were caught up in a crackdown promoted 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."
Italian Premier Giuseppe Conte said he personally contacted Malta's Prime Minister, Joseph Muscat, to "explicitly at least take on the human assistance of persons in difficulty aboard the Aquarius."