The United Nations secretary-general has congratulated Greece for its assistance to more than a million refugees and other migrants who have flowed through the country toward Europe's prosperous heartland.

Ban Ki-moon is in Athens for talks with government officials. Later Saturday he will visit refugee camps on the eastern Aegean island of Lesbos, where most migrants arrive on smuggling boats from Turkey.

Greek Prime Minister Alexis Tsipras presented Ban with an orange life vest jettisoned by migrants arriving on a Greek beach, which Ban briefly donned — the wrong way round.

Some 3,400 of the 57,000 people stuck in Greece live in refugee camps on Lesbos. Most reached Greece after a deal came into effect between the European Union and Turkey on deporting refugees and other migrants back to Turkey.