ROME (Reuters) - Italy’s coastguard on Friday blocked the Sea-Watch 3 migrant rescue ship in the port of Catania citing safety and environmental concerns, delaying the vessel’s plans to return to patrolling the Libyan coastline.

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After a long standoff with the Italian government, on Thursday the Dutch-flagged vessel, run by a German charity, was allowed to disembark 47 migrants it had rescued at sea on Jan. 19 in the Sicilian port.

Coastguard inspectors who boarded the Sea-Watch on Thursday found “irregularities” relating to safety and environmental standards. “Until they are resolved, the vessel cannot leave the Catania port,” the coastguard said.

Italy’s populist government, which took office last year, has closed the country’s ports to the charity ships and insists that migrants be redistributed among European Union partners, a process that often requires lengthy talks.

While Italy has seen 650,000 boat migrant arrivals since 2014, only about 200 have been counted so far this year.

Interior Minister Matteo Salvini, who ordered the port closures, has called for magistrates to put the ship’s crew under criminal investigation.

“It’s obvious there is high (political) pressure to criminalize us,” said Ruben Neugebauer, a Sea-Watch spokesman.

“Blocking the Sea-Watch 3 is part of a longstanding and coordinated Italian government action against sea rescue organizations,” Sea Watch said in a statement. “Sea-Watch points to this as a clear and deliberate political move, designed to prevent us from conducting rescues.”

The humanitarian group had wanted to make repairs and a crew change quickly in order to return to the search-and-rescue area where migrants are often found drifting in overcrowded and unsafe boats, en-route for Europe.

Sea-Watch 3 is the only ship patrolling the area. Most of the others, more than 10 ships at one point, have withdrawn amid political and judicial pressure.

Transport Minister Danilo Toninelli, who is in charge of the coastguard, said the Sea-Watch 3 should not be rescuing migrants because it is registered as a “pleasure yacht” in the Netherlands.

“If you are a millionaire and you buy a yacht, you sail for pleasure, not to be a substitute for the Libyan or any other nation’s coastguard,” Toninelli said on Twitter.