Greece has promised to step up efforts to protect migrants and refugees over the winter on the Greek islands, but defended a 2016 deal between Turkey and the European Union to stop the westward flow of migrants into Europe.

On a visit to France, Prime Minister Alexis Tsipras told the country's Figaro newspaper Thursday that the agreement was difficult but necessary.

His remarks followed strongly criticism from aid agencies and human rights groups over conditions at migrant shelters on Lesbos and other Greek islands.

Greece has seen a surge of migrant arrivals in recent months.

On Thursday, Greek border police recovered the body of a man believed to be a migrant in a river that divides Greece and Turkey — the second such incident in two days.