Updated

Italian prosecutors on Friday investigated alleged threats by some of the 67 migrants against a tugboat crew who rescued them at sea off the Libyan coast.

The Italian coast guard vessel Diciotti had arrived in the port of Trapani, in western Sicily, on Thursday, but the migrants were kept aboard for several hours. Interior Minister Matteo Salvini had vowed that "delinquents" among the migrants would be jailed, then expelled, leaving it unclear if the other passengers would be allowed off to seek asylum.

The Vos Thalassa, an Italian tug assisting an oil rig, rescued the migrants from a human traffickers' boat on Sunday. But the captain then requested the Italian coast guard take the migrants, alleging that some had surrounded some crew and were threatening harm if the tug took them back to Libya.

Salvini insists that the Libyan coast guard deal with migrants in waters off the largely lawless North African country. The tug's captain said when the migrants aboard realized the tug was headed south to put them in the hands of Libyan authorities, some rebelled.

U.N. officials and human rights advocates say migrants are at risk for torture, beatings, rape and other atrocities in Libyan detention centers.

Two African migrants were escorted off the Diciotti Thursday night by Italian police. The other migrants, including young children and women, one of whom reportedly had an injury, were then allowed down the gangway and taken to a center for identification.

Salvini had said a Sudanese and a Ghanaian among the migrants allegedly tried to hijack the tug so it wouldn't return them to Libya.

Italian media quoted Trapani Prosecutor Alfredo Morvillo as saying the investigation would be carried out without bowing to any political pressures. Prosecutors were reviewing statements migrants gave to police.

No arrests were immediately made.

After President Sergio Mattarella expressed humanitarian concerns about the migrants, authorities granted the Italian ship docking permission.

More than 600,000 migrants have been brought to Italy after being rescued in the Mediterranean Sea in the last few years. Salvini is determined to keep new migrants from reaching Italy.

"I'm going all the way so that justice is served," Salvini told the Italian radio station RTL on Friday. He insisted that no more "fake refugees" would arrive, referring to the large percentage of migrants who see their asylum bid fail.

The Italian news agency ANSA quoted a social worker for UNICEF, the U.N. children's advocacy agency, and the aid group InterSos as saying the migrants recounted several minutes of "great confusion and fear." Sahar Ibrahim was also quoted as saying that migrants said they were ready to dive into the sea to avoid being sent back to Libya.

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Frances D'Emilio is on twitter at www.twitter.com/fdemilio