ROME (DPA) - Italian prosecutors ordered on Tuesday (Aug 20) the immediate disembarkation of migrants on board the Open Arms, a Spanish charity vessel stranded off Italy's Lampedusa island.

The decision seemed set to end a nearly three-week stand-off that again exposed intra-EU divisions on migration, amid warnings that the situation on the ship was getting out of control.

The order was given by the Agrigento prosecutor's office after an onboard inspection by its chief prosecutor, Luigi Patronaggio, the Ansa news agency reported.

Interior Minister Matteo Salvini, a migration hardliner who refused to let the Open Arms reach Italian shores, previously said he was expecting the move in a Facebook video.

"The Agrigento prosecutor's office is about to order the impounding of the ship and the disembarkation of the people (on board)," he said.

Salvini also said he expected to face accusations of abuse of office for failing to guarantee adequate health and safety conditions on the rescue vessel.

The Open Arms has been anchored just off the island of Lampedusa since Aug 15, with no permission to enter port, and its passengers have been increasingly frustrated by the blockage.

On Tuesday, 15 migrants jumped into the sea in a desperate effort to reach the shore, Open Arms said in several tweets. They were picked up by the Italian coastguard and taken to the island.

Another two migrants were evacuated for medical reasons, Ansa said.

This left 81 people aboard.

According to Ansa, the migrants swam in rough seas and risked drowning.

The drama led Patronaggio to carry out an inspection on the vessel, it added.

"The situation is explosive, I have to restore calm and ensure that nobody gets hurt," the prosecutor was quoted as saying before leaving from Agrigento to Lampedusa via helicopter.

Before Italian prosecutors acted, the Spanish government said it would dispatch a naval ship to accompany the Open Arms to Mallorca, where its passengers could have been disembarked.

Spain this week offered to accept the ship in one of its nearest harbours - Mallorca or Menorca - but Open Arms said it would not be able to make the journey alone after spending so many days at sea.

Salvini had insisted it was Spain's responsibility to solve the case.

"Spanish NGO, Spanish ship, Spanish port: that's how it should be," he said in a statement.

He motivated his hardline stance by saying that Italy could not become "Europe's refugee camp," even after six EU nations said last week they were ready to take in the migrants after disembarkation.

The six are France, Germany, Luxembourg, Portugal, Romania and Spain.

Open Arms is operated by a charity with the same name. It warned the situation on board had gotten "out of control" on Tuesday, with water and food subject to rationing.

The Open Arms vessel has conducted a series of sea rescues since Aug 2. On Monday, an Open Arms representative had suggested letting the migrants disembark in Italy and flying them to Spain.

Italy offered to take the migrants to Spain aboard coastguard units.

In return, Infrastructure Minister Danilo Toninelli asked Spain to ground the vessel by withdrawing its flag.