Five members of international aid groups have gone on trial in Greece for allegedly attempting to illegally bring migrants into the European Union country.

The three Spanish and two Danish men were arrested in January 2016 on the eastern Aegean Sea island of Lesbos, where the trial started Monday.

They have all denied wrongdoing, arguing that they were on the island to help migrants who were facing dangers at sea.

Lesbos for years has been at the heart of Greece's immigration crisis. It is the main point of arrival for refugees and migrants crossing from the nearby Turkish coast in flimsy boats provided by smuggling rings.

International humanitarian groups have a strong presence on the island.