Spanish Prime Minister Pedro Sanchez, who took office just over a week ago, has given instructions for the boat to be admitted to the eastern port of Valencia after Italy and Malta refused to let it dock.
Spain offered on Monday to take in a rescue ship that is drifting in the Mediterranean Sea with 629 migrants on board after Italy and Malta refused to let it dock.
The Aquarius ship picked up the migrants, including 123 unaccompanied minors, 11 other children and seven pregnant women, from inflatable boats off the coast of Libya at the weekend.
Spanish Prime Minister Pedro Sanchez, who took office just over a week ago, has given instructions for the boat to be admitted to the eastern port of Valencia, his office said in a statement.
Malta on Sunday reiterated its refusal to accept the ship, ignoring calls from Rome.
Italy's hardline interior minister Matteo Salvini, in a joint statement with Danilo Toninelli, minister in charge of the Italian coastguard, insisted that Malta "cannot continue to look the other way when it comes to respecting precise international conventions on the protection of human life."
"That's why we ask the government in Valletta to take in the Aquarius in order to offer first aid to the migrants on board."
Malta's government replied saying Prime Minister Joseph Muscat had spoken to Italian premier Giuseppe Conte and underlined "that Malta is acting in full conformity with its international obligations."
"As such Malta will not take the said vessel in its ports."
TRT World's Jemima Walker has more.
SOS Mediterranee tweeted late on Sunday that the Aquarius had "received instructions from the Italian Maritime Rescue Coordination Centre to standby in our current position which is 35 nautical miles from #Italy and 27 nautical miles from #Malta."
UPDATE La nave #Aquarius ha ricevuto l’istruzione dal Centro di coordinamento del soccorso marittimo (MRCC) di Roma di restare in standby nella posizione attuale (35 miglia dall’Italia e 27 miglia da Malta).— SOS MEDITERRANEE ITA (@SOSMedItalia) June 10, 2018
Conte said that Italy has sent two patrol ships with doctors on board "ready to intervene and ensure the health of anyone on board the Aquarius who might have the need."
Speaking to AFP, a Maltese government spokesman insisted that the rescue of the migrants took place in the Libyan search and rescue area and was headed up by the rescue co-ordination centre in Rome, meaning Malta has no legal obligation to take in the migrants.
Earlier, Aquarius crew member Alessandro Porro told news channel Sky TG24, that the ship was north of Malta and had "received no communications from the Maltese authorities."
"The people we saved yesterday were in a difficult condition, at least 50 were at risk of drowning. We need to have an idea of what port to go to, something that up to now we haven't had."
The migrants were rescued in six separate night-time operations in the central Mediterranean on Saturday.
The French organisation said that 123 unaccompanied minors, 11 small children and seven pregnant women are among those brought on board.
Italy's spat with Malta began after its reported refusal to come to the aid of another rescue ship Seefuchs, which was stranded with 126 migrants on board due to violent seas until it was allowed to dock at the Sicilian port of Pozzallo on Saturday.
EU rules mean migrants must apply for asylum in the European country where they first arrive, putting pressure on Italy and Greece, the entry points for hundreds of thousands of people fleeing war and poverty in the Middle East, Africa and Asia since 2015.
"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," Salvini told reporters.
In the meantime, some in Italy have offered to take in the migrants, with the mayor of Taranto, Rinaldo Melucci, saying that the southern port city was "ready to embrace every life in danger."
"Our land has always been one of refuge, I don't know how you can send away 629 human lives," he added.
Mayor of Naples Luigi de Magistris said on Twitter that "if a minister without a heart leaves pregnant women, children, old people, human being to die, the port of Naples is ready to welcome them."
Italian authorities held the migrant rescue boat Sea-Watch 3 for 12 hours after it brought 232 people to Reggio Calabria, on the southwestern tip of the mainland, at the weekend.
Police questioned the boat's captain for more than four hours, according to Sea-Watch – the NGO that operates the vessel – and journalists aboard were asked to hand over video footage of the June 5 rescue operation.
Sea-Watch said it requested help from the coastguard in Malta to send boats to aid the rescue mission but Malta refused.
German Chancellor Angela Merkel on Sunday called for an EU-wide border protection force, as well as a joint asylum authority and collective standards for granting or refusing applications for protection.
EU leaders in December had set an end-of-June deadline for an overhaul of rules to create a permanent mechanism to deal with migrants in the event of a new emergency.
The summer of 2016 saw a surge in mass drownings in the Mediterranean as Europe's worst migration crisis since World War II peaked with hundreds of thousands of people fleeing war and poverty in the Middle East and elsewhere.