France announced plans Thursday to evacuate three migrants from the Ocean Viking rescue ship in need of urgent medical care, plus one caregiver, amid a standoff with Italy over where the rest of the passengers should disembark.

The decision, announced by the maritime agency directed by Prime Minister Elisabeth Borne, came after the SOS Mediterranee charity that operates the ship requested the evacuations because of Italy's refusal to offer port access.

France insists that under international maritime law, Rome must grant access to the ship and the 234 distressed migrants it rescued.

Italian authorities say other EU nations need to shoulder more of the burden of taking in the thousands of migrants trying to reach Europe from North Africa, often with help of smugglers crowding them into rickety vessels.

"One of the patients is unstable and no longer reacting to treatment since October 27," a spokeswoman for SOS Mediterranee told AFP.

"The two others were injured in Libya and because of this long wait for treatment, they risk having long-term health issues," she said.

The charity has also asked France to open its ports for the other migrants in the wake of Italy's refusal to grant access, so far without an official response.