ATHENS, Greece — Greek authorities say 139 vulnerable asylum-seekers who had been living in overcrowded Greek island camps have left for Germany, as part of efforts to ease overcrowding and move refugees to other European countries.

The group that flew out of Greece on Wednesday consisted of children suffering serious health problems and their immediate families, as well as 53 unaccompanied minors, the migration ministry said.

The unaccompanied minors are part of a program for 1,600 children up to age 18 who are in Greece without their parents or guardians to be resettled in other European countries.

Alternate Migration Minister Giorgos Koumoutsakos said the flight to Germany was the first resettlement flight after Greece's largest refugee camp, the notoriously overcrowded Moria camp on the island of Lesbos, burned down earlier this month.

Greek authorities arrested six Afghans, including two unaccompanied minors, on suspicion of arson. Officials have said the blazes were deliberately set during protests against lockdown and isolation measures imposed to contain a coronavirus outbreak in the camp.

The German government said 51 of the unaccompanied children previously lived in Moria. Germany agreed to take up to 150 children after the squalid camp was destroyed, part of a European pledge to take in 400. The children were transferred to the Greek mainland immediately after the fire.

"We saw terrible pictures in recent days...from Lesbos, from a member state of the European Union. I believe it was right the way Germany acted there and provided humanitarian help, even though we know that it's not a sustainable solution to the problem," German Chancellor Angela Merkel told lawmakers Wednesday.

Merkel said she was "grateful" for a recent European Commission proposal on migrant policy to tackle "a really complicated problem that won't just occupy us for two, three years but, I predict, the entire coming decades."

"If we continue not to have a common basis among the member states of the European Union on the question of migration, then that will be a heavy burden for Europe's ability to act," she added.

The flight that landed in Hannover on Wednesday also carried 17 sick children and their close relatives who were brought to Germany under a commitment that pre-dates the Moria fire to take in 243 children who need medical treatment, the German Interior Ministry said.

In a unilateral move, Germany's government has also said that it will take in 1,553 asylum-seekers — 408 families with children — from various Greek islands who already were granted protected status in Greece.

Just over 26,000 refugees and migrants live in camps on islands, where they arrived after crossing from the nearby Turkish coast in smuggling boats. More than half are on Lesbos.

On Tuesday, authorities moved nearly 1,000 refugees from eastern Aegean islands to the mainland to reduce overcrowding on the island refugee camps.

Officials said all unaccompanied minors in camps on the islands or on Greece's land border with Turkey have been moved to appropriate facilities on the mainland.