Italy has ordered migrants and refugees on board a rescue ship off its coast to be quarantined on another vessel to test them for the coronavirus before allowing them to disembark.

The Alan Kurdi, run by the German non-governmental group Sea-Eye, is sailing in international waters off the western coast of Sicily after rescuing 150 people off Libya's coast last Monday.

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On Sunday, Italy's transport ministry said in a statement that those on board would be screened by health authorities after being transferred and quarantined on that ship.

Last week, Italy closed its ports to NGO vessels rescuing migrants and refugees in the Mediterranean for the entire duration of the national health emergency enforced due to the coronavirus pandemic, a ban due to remain in effect until July 31.

The transport ministry statement said allowing the migrants to disembark without being screened would put too much pressure on already stretched health services in Sicily.

It gave no details on the planned transfer, its timing or location.

The development comes three days after Libya refused entry to about 280 returning migrants whose boat was intercepted by the country's coastguard in the Mediterranean as they attempted to cross into Europe.

According to the International Organization for Migration (IOM), the situation was "tragic" as it called for "a comprehensive approach to the situation in the central Mediterranean".

"The status quo cannot possibly continue," said IOM official Federico Soda.

Libya acts as a major gateway for African migrants hoping to reach Europe. Currently, there are close to 700,000 refugees and migrants in the war-torn country.

More than 16,700 people have died crossing the Mediterranean for Europe since 2015, including at least 241 this year.

More than 500 migrants departed from Libya in the last few days, attempting to reach Europe, according to the IOM. In addition to those intercepted and rescued, 67 reached the Italian island of Lampedusa, where they entered a two-week quarantine because of COVID-19.

At least 70 have been stranded at sea for days awaiting rescue after drifting into Maltese territorial waters, according to Alarm Phone, a crisis hotline for migrants in distress in the Mediterranean.

"The people on board tell us they are 'without water, the pregnant woman is so tired, the child is crying, so thirsty. Please if you don't want to save us give us at least water'," Alarm Phone said in a press release on Saturday.

"In the central Mediterranean, a dangerous rescue gap is actively being created."

At 17:44h CEST, the people on board tell us: "We do not have enough energy left to take the water out of the boat. Our phone battery will die soon." RCC Malta refuses to listen to us on the phone and hangs up. — Alarm Phone (@alarm_phone) April 12, 2020

On Friday, 64 migrants rescued from a capsizing boat in the Mediterranean Sea were brought ashore in Malta, hours after the government had said no further groups would be allowed in after it shut its ports due to the coronavirus pandemic.

The migrants were rescued early on Friday by the Maltese armed forces from a boat inside the Malta rescue zone south of the island.

Malta's government said it could not guarantee further rescues and would not allow any further disembarkation of rescued people because resources have been strained by the coronavirus pandemic.

In a joint statement, 13 NGOs working with migrants and refugees said they are "shocked" by Malta's announcement.

"It is unacceptable for Malta to exploit the COVID-19 pandemic to shelve its human rights obligations and endanger the lives of men, women and children," the statement read.

"Whilst we appreciate Malta's current challenges, we nonetheless insist that migrants must not be sacrificed for the nation's well-being. National emergencies should be overcome with solidarity and compassion," it continued.

"We therefore urge Malta to ensure the rescue and disembarkation of persons within its responsibility and to revise the situation of hundreds of detained persons."