ABOARD THE ASTRAL (AP) — A Spanish rescue ship has set sail for international waters, carrying four European parliamentarians as EU nations bicker over managing migrant flows across the Mediterranean Sea.

The Astral departed Malta early Thursday to join the Open Arms rescue ship already in the search and rescue zone off the coast of Libya. Both are operated by The Spain-based NGO Proactiva Open Arms.

Three Spanish and one Italian lawmaker joined the mission as observers and plan to share their accounts at the next European plenary session July 2-5 in Strasbourg.

Astral's captain Riccardo Gatti says he is not sure the boat will be allowed back into Maltese port. Several charity-run rescue ships have been denied port in Italy and Malta in recent weeks.