Three girls and a woman died after a dinghy transporting migrants from the coast of Turkey sank on Tuesday near the Greek island of Chios, Greek authorities said.
Another 22 people – 14 men, seven women and a child – were rescued from the sinking boat which had set out in strong winds, the Greek coastguard said.
Three helicopters, two coastguard ships and at least six private boats took part in the rescue operation.
Initial reports, including a tweet from Migration Minister Notis Mitarachi, said the victims were all children but that was later updated to three girls and a woman.
"Tragically, in spite of the best efforts of the Hellenic coastguard, four children – all between the ages of 3 and 14 – are confirmed dead, one person is missing, 22 were rescued and are being cared for ashore," Mr Mitarachi tweeted.
"The Turkish authorities must do more to prevent exploitation by criminal gangs at source. These journeys should never be allowed to happen.”
The minister accused Turkey of failing to observe its 2016 agreement with the European Union to try to keep migrants from setting sail for EU territory from Turkey.
Merchant Marine Minister Yiannis Plakiotakis said the smugglers had shown "criminal disregard for human life".
The United Nations' refugee agency UNHCR says more than 2,500 people have crossed the Aegean from Turkey this year, and more than 9,700 in 2020.
More than 100 people died or are missing after migrant boats sank last year, the agency says.
Greece blames Turkey for not taking sufficient action to curb smugglers who launch migrants in unsafe boats and dinghies from its shores.
Turkey, which hosts about 4 million refugees, says the EU has been slow to deliver on promises of financial support.