The Spanish decision came just hours after the European Union and the United Nations refugee agency had called on Italy and Malta to let the rescue ship in and end the standoff after the two governments traded accusations of not doing enough amid the migrant crisis.
By law, it would have been hard for Italy to refuse the boat a safe haven, as its own Coast Guard co-ordinated the rescues, picking up more than 280 migrants in its own vessels before transferring them to the Aquarius to be taken to safety.
The ship, which is severely overloaded, is operated by SOS Méditerranée and Médecins Sans Frontières (MSF).
Antoine Laurent said on Monday it would take at least two more days for the vessel to make it there and that "is not possible today with 629 people on board".
"The people we saved yesterday were in a hard condition, at least 50 were at risk of drowning".
"Our objective is the disembarkation in a port of safety of the 629 people now on board the Aquarius - some we rescued yesterday night in hard conditions", she said.
Refugees International is dismayed by the Italian government's refusal to allow the SOS Mediteranée and Médecins Sans Frontières (MSF) ship, the Aquarius, to disembark in Italy.
The leaders of Italy and Malta are thanking Spain for allowing a rescue ship with 629 migrants aboard to dock in Valencia. "Encouraging change in humanitarian policy from (Sanchez's) government", Barcelona Mayor Ada Colau wrote on Twitter after the government's offer. "All a political stunt.at the expense of people in distress?"More news: Eid-il-Fitr: FG declares Friday, Monday public holidays
"Given the boat's location, it is between Italy and Malta", he added. Efforts by Rome to persuade other EU states to accept some of the newcomers and share the cost of their care have largely fallen on deaf ears, heightening anti-European and anti-migrant sentiment in the Italy. During the Italian general election this March, the League party and its allies campaigned on a nationalist, anti-immigration platform and won a plurality of seats in Italy's legislature. "Italy has stopped bowing our heads and obeying", Salvini said in a Facebook post.
Among those on board are 400 migrants rescued by the Italian navy and merchant vessels before being transferred to the Aquarius.
"There is a degree of cynicism and irresponsibility in the Italian government's behaviour with regard to this dramatic humanitarian situation", government spokesman Benjamin Griveaux quoted Macron as telling his cabinet.
"If a boat had France as its closest coast, it could land", Griveaux said. "The Mediterranean is the sea of all the countries that face it, and it (Malta) can't imagine that Italy will continue to face this giant phenomenon in solitude". The aid group said the migrants were "exhausted and stressed" and warned of severe health risks to a number of the passengers during the 1,500-kilometer journey, expected to take three to four days. Conte said he would discuss the situation further with Salvini and other ministers on Monday evening.
"This is not an inhumane act", said Transport Minister Danilo Toninelli, in charge of Italy's ports and coastguard.
The Valencia option was satisfactory for Italy, whose new populist government has taken a hard stand against immigration. On Monday afternoon, Spain offered to take the ship. "It's unacceptable to play politics with human lives which is what is happening at the moment", Gabriel Attal told the Public Senat channel.
"The position, the line of the Italian government is sickening". The mayor of Naples, who has repeatedly clashed with the League leader, said he would welcome in the humanitarian boat.