Sea-Watch 3, operated by a German aid group, could be seen about a mile offshore from Syracuse, Sicily as fishermen, priests and others turned out for a solidarity rally in support of the stranded passengers.
The ship rescued the migrants on Jan.19, but Italian Interior Minister Matteo Salvini has refused to let private rescue boats into the country's ports. Salvini has argued the vessels' presence on the Mediterranean encourages human traffickers.
Italian authorities said the people on the Sea-Watch 3 were picked up in an area that is within Libya's search-and-rescue jurisdiction. They allowed the ship to shelter in Italy's territorial waters Thursday as the weather worsened farther out.
The mayors of Naples and Palermo have offered their ports, but national authorities hold jurisdiction. Germany aid group Sea-Watch has said several migrants were spending cold nights above deck due to space constraints and at risk of being swamped overboard by waves.
The passengers include 13 unaccompanied minors aboard, according to the U.N. agencies. A juvenile court judge in Catania urged the government Friday to grant the rescue ship permission to disembark them.
Sea-Watch spokeswoman Giorgia Linardi said the cramped conditions in the 20-square-meter (200 square feet) space below deck reminded some passengers of the detention facilities in Libya where they awaited an opportunity to embark for Europe in smugglers' rubber dinghies and wooden fishing boats.
Aboard Sea-Watch 3, "they are amassed in a cold room, a mile from the coast" of Italy, Linardi said. The U.N.'s International Organization for Migration, refugee agency UNHCR and UNICEF, which is concerned with children's welfare, expressed "grave concern" and said that "this situation can't drag on for long, above all in a difficult period like winter."
"The absolute priority remains that of saving human lives and guaranteeing a port of safe disembarkation and adequate assistance to those who have already risked life aboard flimsy vessels," the three agencies said in a joint statement Saturday.
Italy has equipped the Libyan coast guard to better intercept trafficked migrants. U.N. officials and human rights advocates say returning rescued migrants to largely lawless Libya will expose them again to torture, rape, overcrowding and scanty rations.
Maritime law specifies that boats are supposed to bring rescued people to the nearest safe port, and human rights advocates have argued that Libya isn't safe for detained migrants. In a statement on Twitter, Linardi said a 24-year-old Gambian man on Sea-Watch 3 bears a scar from forehead to chin. She said he was slashed in Libyan detention, where his hands were tied to a ceiling, according to a video sent to his relatives.
Rescued migrants have told Italian authorities that smugglers often call migrants' families to hear screams of pain in hopes they'll send more money to the traffickers. "Until Libya is considered a safe port, all European states should finally show a sense of responsibility and solidarity," the U.N. statement said.
The agencies called for "the current 'boat-by-boat' approach" to be replaced with a "mechanism for safe and orderly disembarkation in the central Mediterranean."
Frances D'Emilio is on twitter at www.twitter.com/fdemilio