Updated 9.15pm
An Italian prosecutor on Tuesday ordered the more than 80 remaining migrants on the Open Arms charity vessel to disembark in Sicily after it was stuck for days off Lampedusa.
Luigi Patronaggio also ordered the vessel preventatively seized after inspecting the boat on which some of the migrants have spent 19 days and "given the difficult situation on board", a judicial source said.
The ship has been stranded off Lampedusa for six days, with Open Arms saying the situation on board was "untenable".
Patronaggio ordered the ship seized as part of his probe into alleged kidnapping and refusing to obey orders targeting far-right Interior Minister Matteo Salvini
"If anybody thinks they can scare me with the umpteenth complaint and wants a trial, they're mistaken," Salvini said on Facebook.
Many rescued migrants have jumped in the sea in a bid to swim to land as the latest standoff between a charity vessel and Salvini continued.
Meanwhile, a Spanish navy patrol boat set sail on Madrid government orders Tuesday evening on a three-day voyage across the Mediterranean to pick up the migrants on the Open Arms.
The Open Arms is currently anchored off the coast of the Italian island of Lampedusa where authorities had been refusing to allow it to dock.
It posted videos on Twitter showing migrants attempting to swim to the coast after leaping overboard.
"Nine people have thrown themselves into the water desperately trying to reach the coast of Lampedusa," the NGO said in a tweet.
"Our Italian lifeguards and coastguards are trying to rescue them. The situation is out of control."
It later said around 15 in total had jumped overboard and some had been rescued and taken to Lampedusa.
The Open Arms has been stuck in the Central Mediterranean for more than two weeks amid a stand-off with Italy's interior minister, Matteo Salvini, who is refusing to allow it to dock.
Is this an end to the migrant crisis?
In a statement, the Spanish government signaled there could be an end to the crisis as it announced that a military ship 'The Audaz' would leave on Tuesday afternoon to "take charge of the people taken in by the Open Arms".
However, it said the ship would take three days to reach Lampedusa as the Open Arms warned the situation on board was now "out of control".
The Spanish patrol boat will escort the Open Arms charity ship back to the port of Palma in the Balearic Islands.
"After analysing various options, the Spanish government... considers this is the most suitable" for "the humanitarian emergency on board the Open Arms."
Some of the migrants have been stuck for 19 days after being rescued at sea off the coast of Libya.
The vessel has been anchored since Thursday within swimming distance of Lampedusa, seeking permission to dock, with the situation increasingly tense.
There were initially 147 migrants on board but as the days have passed, some were evacuated for medical care and all minors were allowed to disembark.
What will happen to those on board?
Six European Union countries, France, Germany, Romania, Portugal, Spain and Luxembourg, have offered to take in the migrants.
But Italy's far-right Interior Minister Matteo Salvini, who has plunged the Italian government into crisis by calling for fresh elections, refused to allow migrant rescue vessels to dock as part of his hardline policies.
The NGO has also said Malta ignored its appeal for help.
Faced with Italy's protracted refusal to allow the migrants to disembark, Spain at the weekend offered up its southern port of Algeciras, which the NGO said could "not be achieved" due to the distance and tensions on board.
Madrid then offered up Mallorca in the Balearic Islands, nearer but still around 1,000 kilometres (600 miles) from Lampedusa.
The charity described this offer as "totally incomprehensible" and continued to demand the ship be allowed to dock in Lampedusa.
Spain's Defence Minister Margarita Robles has slammed Italy, and particularly Mr Salvini, for the situation.
"What Salvini is doing in relationship with the Open Arms is a disgrace to humanity as a whole," she said Monday.
Mr Salvini "has shown he doesn't care about human lives", she added Tuesday.
Mr Salvini, who serves as Italy's deputy prime minister, tweeted that "being firm is the only way to stop Italy from becoming Europe's refugee camp again."