A charity rescue vessel on Saturday brought 41 shipwrecked migrants into port in Lampedusa, the second boat to defy far-right Interior Minister Matteo Salvini's bid to close Italian ports to them.
Mediterranea's Italian-flagged Alex was met by a strong police presence on the quayside but people were not allowed to disembark after spending two days with the rescued migrants and asylum seekers on the sailboat.
"I do not authorise any landing for those who couldn't care less about Italian laws and help the people smugglers," populist deputy prime minister Salvini tweeted as night fell.
Salvini last month issued a decree that would bring fines of up to 50,000 euros (USD 57,000) for the captain, owner and operator of a vessel "entering Italian territorial waters without authorisation".
After the Alex reached port, he said that he would raise the maximum fine to one million euros.
Mediterranea tweeted back a request to disembark those rescued, saying it had sailed to "the only possible safe port for landing", citing "intolerable hygiene conditions aboard".
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"Shipwrecks and crew are exhausted... people rescued need to be cared for... this is a surreal situation and it is an unnecessary cruelty to prolong the wait." Authorities on Lampedusa last week seized another rescue ship belonging to German aid group Sea-Watch after it forced its way into port with dozens of rescued migrants on board and arrested its captain, Carola Rackete.
An Italian judge this week ordered her freed as she had been acting to save lives, a decision which sparked Salvini's ire but may have encouraged the Alex crew.
Two other investigations, on charges of helping people smugglers and resisting the authorities are still under way after Rackete forced her way past Italian customs vessels.
A third rescue ship, German charity Sea-Eye's vessel Alan Kurdi, carrying 65 shipwrecked migrants rescued off Libya had also arrived in international waters off Lampedusa.
The group said late Saturday that it was heading for Malta.
In Germany, more than 30,000 people demonstrated in cities around the country in solidarity with Rackete, including 8,000 in Berlin and 4,000 in Hamburg.
"The irresponsibility of European countries obliged me to do what I did," Rackete said in a message to demonstrators, many of whom brandished life vests.
German Interior Minister Horst Seehofer wrote a letter to Salvini asking him to rethink his policy, sources close to the German government said.
"We cannot be responsible for boats with people rescued from shipwrecks on board spending weeks on the Mediterranean because they can't find a port," Seehofer wrote.
Salvini accuses NGO rescue vessels of helping smugglers and had insisted the Alex sail for the Maltese capital Valetta after 13 "vulnerable" people were on Friday taken to Lampedusa, leaving 41 on board.
Malta also told the Alex to go to Valletta to disembark the migrants, but Mediterranea said the journey would be too arduous and the boat would likely be seized if it did.
Photographs showed dozens of migrants and asylum seekers seeking shelter from the sun under survival blankets on the narrow deck of the 18-metre (59-foot) sailboat.
"In these conditions it is impossible to face 15 hours of sailing,"