MADRID, April 16 (Xinhua) -- An Italian judge on Monday ordered authorities on the island of Sicily to release the Spanish vessel Proactiva Open Arms which was seized last month.

The vessel belongs to the Spanish charity Open Arms and is used to rescue migrants attempting to cross the Mediterranean Sea between North Africa and Europe.

The ship had been confined to port since March 18 after being seized and its crew charged with promoting "illegal immigration and criminal association," following an incident with the Libyan coast guard in international waters, 70 nautical miles off the coast of the African nation.

The crew of the Proactiva Open Arms refused to hand over 218 migrants they had just rescued to the Libyan authorities and instead took them to port in Sicily.

The Italian Public Prosecutor determined the crew had "violated the law and international agreements by not handing the migrants to Libyan authorities."

Oscar Camps, the charity's founder explained at the time that had he handed the migrants over the Libyan authorities it would have been "equivalent of a summary deportation."

The action of the Italian authorities saw the launch of an online petition which was signed by over 300,000 people demanding the ship's release.

Camps posted a tweet on Monday celebrating the release of the ship, but explained it was "only a first step," and that the "investigation into forming part of a criminal organization and promoting illegal immigration" were still ongoing.

Those charges carry possible prison sentences of between four and seven years.

The International Organization of Migration calculated that 3,116 migrants died attempting to cross the Mediterranean Sea in 2017, while figures released last week showed that one in 27 immigrants trying to cross to Spain in the three months of 2018 died in the attempt.