Ban praised Athens for showing "remarkable solidarity and compassion" towards refugees, but urged other countries to work on the issue.

"Greece should not be left alone to address this challenge on its own," Ban told reporters after meeting Prime Minister Alexis Tsipras. Over the past year and a half, more than 1 million refugees, many coming from Syria, have arrived on the Greek islands.

In a symbolic move, Tsipras presented the UN General Secretary with an orange life vest discarded by migrants upon landing in Greece (photo).

"It's a symbolic gift, a life-saving tool for thousands of refugees who arrived in the Greek islands after crossing the Aegean Sea," Tsipras said.

Ban meanwhile hailed Greece for managing the refugee influx at the same time as grappling with its debt crisis.

"Despite the country's economic difficulties, Greece has been saving human lives," he said, adding that country deserves the support of the international community "and should not be left on its own to face this challenge."

The UN is due to hold a meeting on the global refugee crisis in September, with world leaders discussing a new plan to resettle the migrants. Ban Ki-moon had previously said that the world had to address the "biggest refugee crisis of our time."

Next stop: Lesbos

Ban Ki-moon was due to visit the island of Lesbos as the next stopover on his itinerary - a key destination for migrants attempting to cross the Mediterranean from Turkey. According to UN figures, Lesbos alone accounted for around 500,000 arrivals in 2015.

Over a million migrants have sailed to Greek shores since January 2015, while thousands have drowned at sea. The rate of migration has fallen drastically since March this year due to an EU deal with Turkey. At the same time, the Balkan states, situated north of Greece, started closing their borders to newcomers, effectively cutting off their path towards Western Europe.

The government in Athens said that some 56,000 migrants are still trapped in the country, including some 3,400 in Lesbos. Human rights activists claim that the migrant camps are poorly equipped and unsuitable to house migrants for longer periods.

dj,ss/jm (dpa, Reuters, AFP)