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LONDON — Pope Francis has pleaded for European leaders to help 49 migrants stranded at sea after two rescue boats were refused permission to dock in both Italy and Malta.

“I make a heartfelt appeal to European leaders to show concrete solidarity for these people,” the pontiff told crowds gathered in St. Peter’s Square on Sunday.

Pope Francis celebrates Mass at the Vatican on Sunday. Andrew Medichini / AP

The Dutch-flagged vessel Sea-Watch 3, which is operated by a German humanitarian organization, rescued 32 migrants including women, children and unaccompanied minors off the coast of Libya on Dec. 22.

Sea-Eye, which is another German humanitarian group, said its boat of the same name is also stranded off the coast of Malta after it plucked 17 people from the Mediterranean Sea on Dec. 29.

The doctor aboard Sea-Watch 3 — which has been unable to dock for 16 days — said some of the migrants were seasick and growing increasingly desperate. On Jan. 4, Sea-Watch said one migrant had even tried to jump ship and swim to Malta before he was hauled back on board.

“The situation here on board is getting more and more unstable. Every day the stress level is increasing,” said the doctor who was identified only as Frank in a video posted on Twitter. “It is a very dire situation. This needs to end as soon as possible."

Day 16 without a port of safety: The situation on board the #SeaWatch3 remains critical and does not allow any relaxation. Our doctor Frank gives a short update. pic.twitter.com/5ygeRMHUaO — Sea-Watch International (@seawatch_intl) January 6, 2019

Italy and Malta have clashed over who should take in the migrants with both refusing to open their ports to the vessels despite pressure from humanitarian groups.

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On Jan. 3, Malta allowed the two ships to shelter in port from a storm but it has refused to let the migrants disembark.

Maltese Prime Minister Joseph Muscat said in a statement posted online Sunday that he did not want to set a precedent by allowing the migrants into Malta.

"It’s easy to be the Christmas saint but then come January, February and the summer period we would be told to do the same," Muscat added.

Th Sea-Eye rescue ship docked at the Spanish harbor of Malaga in December. Jorge Guerrero / AFP - Getty Images

Muscat said his country had saved almost 250 people at sea over the Christmas period “without protesting” but that it was not its responsibility to take in these 49 migrants as they were not rescued in Maltese waters.

Italy has also refused to welcome the ships. Interior Minister Matteo Salvini, who also serves as deputy prime minster and who is a member of an anti-immigration populist party, has said the country has taken in “too many fake refugees.”

“Human trafficking must be stopped," he posted on Facebook explaining his decision to keep Italy's ports closed. "People escaping war should come to Italy by plane, as many already do, not by boat. We can send medicines, food and clothes to the boats, but enough of this blackmail."

Filippo Grandi, the U.N. high commissioner for refugees, said the U.N. had received offers from some European states to receive the migrants aboard Sea-Watch 3 and Sea-Eye but gave no further details.

Nevertheless he warned that "unless a shared system of disembarkation and care is agreed upon, protracted negotiations will continue to cause hardship to those suffering and tension in Europe."

Charlie Yaxley, the U.N. refugee agency's spokesperson for Asia and Europe, said "2019 must see an end to the boat by boat approach for allowing ships to dock rescued refugees and migrants."

The ships are not the first to be stranded at sea.

The Aquarius, a rescue ship jointly operated by Doctors Without Borders and SOS Mediterranee, was kept at sea for 10 days in July after being repeatedly refused permission to dock my Italy and Malta.

In December, the two humanitarian organizations which ran the ship said they were ending its operations, blaming harassment from Italy and other countries.

A month before, an Italian prosecutor had ordered the seizure of the vessel on the grounds that crew members had contravened rules for the disposal of waste.

The latest incident follows the implementation of a landmark U.N. agreement in December, in which signatory states agreed to better share the responsibility for migrants across the globe.

The pact, known as the Global Compact for Safe, Orderly and Regular Migration, was signed in Morocco by 164 nations, including Malta. An Italian delegation did not travel to the conference and Salvini has said Italy will debate the agreement in parliament.

Jeff Crisp, an expert in migration at the University of Oxford in England, said the fact that the migrants aboard the rescue ships still hadn't been able to disembark marked a "bleak beginning" for the first year of the agreement with its primary focus on responsibility-sharing.