The U.N. refugee agency expressed alarm Sunday about the fate of dozens of migrants whose rubber dinghies appear to have capsized after setting sail from Libya for Italy.

Two German monitors of dangerous migrant crossings reported spotting four boats in distress off the coast of Malta over the weekend.

A spokeswoman for the United Nations High Commissioner for Refugees (UNHCR) said the fate of two boats was unknown.

"We are very worried," Carlotta Sami told Agence France-Presse (AFP).

"It seems that at least one boat has capsized, and there is no longer any contact with another one."

The European Union's Frontex border guard and coast guard agency declined to comment when contacted by AFP.

The coast guard authorities of Italy and Malta also did not comment on the reported shipwreck.

Germany's Sea-Watch International group said on its official Twitter account that Frontex had spotted the four rubber boats on Sunday.

"One of them capsized," Sea-Watch International said.

"We have to assume that it sank with people on board, since there is no knowledge of a rescue or interception."

It also showed the boats' geolocation, including one boat marked "unknown GPS contact lost."

Sea-Watch presumed that boat was carrying 85 people.

It said the other three boats were carrying 173 migrants in all.

Germany's United4Rescue monitor of migrant crossings said in a statement that it was receiving the same reports and feared for the lives of "dozens."

Italy has long established itself as the primary European port of entry for migrants seeking refuge from Africa and the Middle East.

But the Mediterranean country shut down its ports and said it would quarantine any illegal migrants because of the coronavirus pandemic.

The Swiss-based International Organization for Migration (IOM) said the reports were "very worrying" but difficult to verify.

"In the absence of boats in the area, it is very difficult at the moment to confirm that there has been a shipwreck, or the number of victims involved," IOM Italy spokesman Flavio Di Giacomo told AFP.

"And unfortunately, from experience, we also think it is likely that there have been shipwrecks of which we are not aware."