Italian authorities have seized a Spanish charity’s rescue ship after it brought 216 migrants stranded off the coast of Libya to Sicilian shores.

Proactiva Open Arms picked up the migrants and refused to release them to the Libyan coastguard, which would have returned them to Africa.

A public prosecutor in Sicily ordered the boat’s seizure after it docked in the port town of Pozzallo on Sunday.

Crew members are suspected of criminal association in illegal immigration.

The case highlights tensions between humanitarian organisations rescuing migrants at sea and EU states that have sought to reduce the number of migrants making dangerous boat crossings to reach the continent.

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What happened?

On Thursday, the rescue ship went to help two boats 73 miles off the Libyan coast, after a notification by the Italian coastguard.

However the Italians then told the Spanish group’s ship that the Libyan coastguard was in charge of the operation, according to the AFP news agency.

Proactiva Open Arms’ founder Oscar Camps tweeted that the Libyan patrol boats threatened to open fire on their rescue dinghies and demanded the charity hand over “the women and children” they had rescued.

The group refused.

The Libyan Navy, meanwhile, accused Spanish group of “starting a contest with Libyan coastguards to rescue migrants” in an area where the Libyans are the “legally-mandated authority”.

“The [Proactiva Open Arms] boat had observed the approach of the [Libyan] patrol boats,” said a statement published on Afrigate News website.

“It started to unload two inflatable boats with the aim of reaching the boat carrying the migrants, as if we were not [in the midst] of an operation to rescue humans, but in a [race] to acquire spoils”.

The Libyan coastguard eventually called off its operation.

How did this end up in Sicily?

The charity’s crossed the Mediterranean in search of a port to disembark in. For two days they were denied entry to European harbours. They say this was because of their refusal to hand over the migrants to Libyan authorities.

On Friday, the charity said it took a baby boy and his mother to Malta in an emergency evacuation.

On Saturday, the ship and its remaining 216 migrants were allowed by the Italian coastguard to dock in Sicily.

A day later an Italian prosecutor from the island’s capital Catania ordered the ship’s seizure pending an investigation into three crew members – the captain, the charity’s founder Mr Camps and a co-ordinator.

The prosecutor’s office said Proactiva violated international agreements by bringing the migrants to Italy instead of handing them over to Libyan authorities, according to media reports.

“I guess they’ve instituted the crime of solidarity,” a lawyer representing the ship’s commander said, according to Italian press agency ANSA.

The seizure order comes from the same prosecutor who alleged last year to have evidence of some rescue charities colluding with people-smugglers.

He later said his investigation had found no proof of wrongdoing, according to Reuters.

More than 600,000 migrants have arrived in Italy by sea in the past four years. Immigration was a key issue in an election earlier this month, and voters rewarded an anti-immigrant centre-right alliance with the most seats in the lower house of parliament.