Greek authorities have arrested the captain of a boat that was part of a flotilla bound for the Gaza Strip to deliver humanitarian aid.

The 60-year-old captain – whose name has not been released – was in police custody Saturday for leaving port without permission. The Greek government has forbidden ships docked in its ports to depart for Gaza.

Israel, the United States, European Union and United Nations have all urged international organizers of the flotilla to cancel their plans to try to break the Israeli sea blockade on the Palestinian territory. They have urged the flotilla to sail to Israeli or Egyptian ports and transfer its cargo legally to Gaza over land.

A year ago, Israeli naval commandos intercepted a Gaza aid flotilla, and in the raid, nine pro-Palestinian activists were killed. The incident sparked international outrage and raised regional tensions.

Despite this, activists said Saturday that they still intend to challenge the blockade, saying the blockade is illegal and immoral. Organizers hope to bring up to eight boats and two cargo vessels laden with supplies to Gaza, along with about 300 people, including politicians, journalists, writers and religious figures.

But two boats are disabled, allegedly by Israeli sabotage. The Israeli government vehemently denies it was involved in sabotage.