German NGO Sea-Watch said in a statement that their boat Sea-Watch 3 was held until gone midnight yesterday after arriving at the port at Reggio Calabria with 232 people onboard.
Italian police questioned the boat captain for more than four hours, according to the NGO, and journalists travelling on the vessel were asked to hand over video footage of the rescue operation, which took place on June 5.
"The political attacks against us are not only endangering us, but those in maritime distress," the NGO tweeted.
"After 12 hours stuck in port, without a comprehensible reason given by the authorities, while there were 6 SAR-Cases on the Mediterranean Sea, we finally set sails to SAR." SAR stands for search and rescue operations.
Sea-Watch said police also questioned some of the rescued migrants from the boat. After being processed by the authorities they are likely to end up in migrant reception centres.
The holding of the boat comes after Italy's new anti-immigrant government pledged to slow down landings and speed up expulsions of migrants illegally in the country.
"If anyone thinks I won't move a muscle while we have another summer of landings, landings and more landings, well that's not what i'm going to do," said new Interior Minster Matteo Salvini from the far-right League party yesterday.
Salvini has previously lambasted neighbouring Malta for not doing more to help deal with would-be asylum seekers -- a charge Malta has denied.
While Sea-Watch 3 was being held in Reggio Calabria, fellow NGO SOS Mediterranee rescued 629 people in six separate night-time operations in the Mediterranean.
The French organisation said that of those saved and brought on board its ship Aquarius on Saturday night, 123 are unaccompanied minors, 11 are small children and seven are pregnant women.
They are currently heading north in search of a secure port at which to dock.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)