United Nations Secretary General Ban Ki-moon called on Saturday for countries to do more to help cope with Europe’s migrant crisis, saying Greece could not manage on its own.

Speaking in Athens before heading to the Greek island of Lesbos, the gateway into Europe for nearly a million people last year, Ban said Greece had shown “remarkable solidarity and compassion” in dealing with the hundreds of thousands of migrants fleeing war, despite its economic hardship.

“Greece should not be left alone to address this challenge on its own,” Ban told reporters after meeting Prime Minister Alexis Tsipras.

“We must work together to protect people and address the causes of displacement. I continue to call for a greatest sharing of this responsibility across Europe and indeed across the world.”

About one million people crossed the Aegean Sea from Turkey to Greek islands last year in small and often overcrowded inflatable boats. Hundreds drowned trying to make the crossing.

The migratory shift from Turkey to Greece has slowed to a trickle since March, when the European Union and Turkey reached an agreement for Ankara to seal the route in return for financial and political rewards.

The accord obliges Greece to return to Turkey those migrants who either do not apply for asylum or have their claims rejected.

Officials say about 8,400 migrants are currently on Greek islands, nearly all of whom have expressed interest in applying for asylum, overwhelming the system.

Additionally, there are an estimated 48,000 on the Greek mainland, stuck there after a wave of border shutdowns throughout the Balkans.

Tsipras said Greece had taken a big burden on its shoulders and asked for solidarity so that his country could deal with the situation.

In a symbolic move, Tsipras offered Ban a life jacket, one of thousands of items Greek authorities have recovered from the shores of Greek islands since last year. He hoped the EU-Turkey deal was respected so that refugees and migrants would not need this life-saving tool in the future.