Six children have drowned after a rubber dinghy carrying Afghan migrants to Greece sank off Turkey's Aegean coast, Turkey's state-run news agency said.

The Anadolu Agency said the coastguard rescued five migrants from the sea and were still looking for two others reported missing.

The bodies of the children were recovered. Anadolu did not report their ages, but said one of them was a baby.

The migrants were apparently hoping to make it to the island of Khios from the resort of Cesme despite bad weather.

Turkey has stepped up efforts to stop migrants departing for Greece by sea. Last week, authorities rounded up around 3,000 in the town of Ayvacik, north of Cesme, who were believed to be waiting to make the journey to the Greek island of Lesbos.

The boat sank after wooden reinforcements used to fortify it came apart in the sea, causing it to take in water and sink, Anadolu said.

More than 700,000 migrants have crossed into Greece this year, many fleeing conflict in Syria or Iraq. Nearly all have entered the country from Turkey, paying large fees to smuggling gangs who arrange their crossings in small, overcrowded boats. Hundreds of people have drowned in the Aegean Sea, including dozens of children.

The sweep last week came after Turkey and EU leaders agreed to re-energise Ankara's long-stalled bid to join the 28-nation bloc and bolster their resolve to deal with the Syrian refugee crisis, although authorities would not say if the detentions were directly related to the Turkish commitment to help contain the flow of migrants.

Human rights group Amnesty International criticised the detentions, calling them "alarming".

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