Madrid on Tuesday dispatched the Audaz to take all of the migrants who were aboard the Spanish charity rescue vessel, stuck at sea off the coast of Lampedusa for days because Rome refused to let them set foot on Italian soil.

But just a couple of hours later an Italian prosecutor ordered that the roughly 80 migrants still aboard the Open Arms be allowed to disembark in Lampedusa, raising doubts over the mission of the Spanish navy boat.

"It was useful and more efficient if it finishes its voyage and brings us the quota (of migrants) which corresponds to us," Deputy Prime Minister Carmen Calvo told reporters.

"We don't know if another country can join this distribution at the last minute but in principle our quota was 15 and it is this number of (migrants) we will bring back to our country as part of the humanitarian response," she added.

France has said it will take in 40 of the Open Arms migrants, while Portugal has pledged to take in 10. Germany and Luxembourg also are expected to take some in.

Romania was also willing to accept some of the migrants, but the pledges from the other five nations sufficed.

Many of the migrants had spent 19 days aboard the ship after being picked up while trying to make the perilous voyage from Libya to Europe in small boats.

Initially the Open Arms carried 147 mainly African migrants, but all the minors and some suffering health problems disembarked before the ship was finally allowed to dock in Lampedusa.