A young Syrian boy died after the dinghy he was on collided with a Greek Coast Guard's vessel, authorities confirmed on Wednesday.
The incident took place in the night of Tuesday and Wednesday near Kos, a Greek island off the coast of Turkey.
Thirty-four people were on board the dinghy and one person is still missing, the UN's High Commission for Refugees said on Twitter.
Six of the migrants, including a pregnant woman, were taken to hospital, the Greek Coast Guards said.
The EU's border agency, Frontex, estimated that 885,000 migrants used the eastern Mediterranean route to reach the EU at the height of the migrant crisis in 2015.
The number declined significantly in the following two years following a deal between Brussels and Ankara but increased again in 2018 "due to the increase in land crossings from Turkey to Greece."
Turkey is currently hosting more than 3.6 million refugees.
According to Watch the Med, a migrant rescue NGO, the Aegean Sea has become one of the frequent routes for people attempting to reach Europe.
The NGO also flagged in June that it has noticed "an increase in accounts of attacks by "masked men" in the Greek territorial waters".
"The return of this life-threatening practice of pushbacks, alleged to be by the Greek Coast Guard, puts the lives of people escaping war and conflict into danger once more," it added.