(CNN) Amid the ongoing controversy over immigration, the owners of two rescue boats say Italy has forced them to stop operating.
One of the boats, the Lifeline, has 234 people on board whom it rescued off the coast of Libya and 17 crew members. Italy says it will seize the Lifeline for violating international law.
The other, the Seefuchs, or Sea Fox, docked in Malta after Italy questioned its registration.
The boats are operated by German nongovernmental organizations. Operators insist they are registered in the Netherlands, which has denied responsibility for them.
Danilo Toninelli, the Italian minister of infrastructures and transport, said on Twitter that the Italian government will sequester the Lifeline and investigate whether it is in violation of international laws.
The Lifeline "is without the tools to guarantee safety to the migrants and crew," Toninelli said. "Human lives must be saved, but it must be done legally and safely."
During a Facebook Live post from his office earlier this week, Italian Interior Minister Matteo Salvini said the Lifeline "forcefully boarded 224 illegal migrants in Libyan waters" despite warnings by the Italian coast guard that Libyan authorities were in charge of the rescue. Salvini refused to let it dock in Italy.
The Lifeline insists it is registered with Dutch authorities.
Gorden Isler, a spokesman for Sea-Eye, which operates the Seefuchs, said it "was forced to cease" its rescue mission without picking up any immigrants because Italy questioned the ship's "flag status."
He said the ship is registered as a "pleasure vessel," not for commercial use, so it has suspended operations until it is properly registered.
"After more than two years of intensive cooperation with the Italian and Dutch authorities, this procedure is completely incomprehensible," Isler said.
Previously, the Aquarius, a ship carrying hundreds of rescue migrants, was blocked from docking in Italy. The new populist government demanded that other European nations help deal with the immigration issue despite protests in Rome supporting the migrants.
The Aquarius arrived Sunday in Spain.
It had been left to drift for two days between the Italian and Maltese coasts, becoming a symbol of the migration crisis in the Mediterranean.
This story has been updated with the latest information about the number of migrants on board one of the rescue boats.