The United Nations secretary-general is visiting a charity in Athens, ahead of talks with Greek government officials and a trip to the island of Lesbos, which is at the forefront of Greece's immigration crisis.

Ban Ki-moon met with officials and volunteers at the Solidarity Now group, which helps victims of Greece's financial crisis and migrants stuck in the country.

Later Friday, he was to see Greek President Procopis Pavlopoulos.

On Saturday Ban will visit camps on Lesbos where 3,400 refugees and other migrants live.

The eastern Aegean island was a main arrival point for the more than 1 million people who reached Greece by sea since January 2015, on their way to Europe's prosperous heartland. About 56,000 people are still stuck in Greece after a series of Balkan border closures.