A routine check found “things that were not logical,” Fernandez told Perfil radio on Monday.
“They had declared a crew that was smaller than the one that traveled,” he said, adding the matter was “still under investigation.”
He said the five Iranians were in a hotel.
Officials originally said their passports had been taken but would be returned if they left the country on a scheduled flight while investigations continued into the plane’s origins.
The Venezuelan Boeing 747 cargo plane reportedly carrying car parts first landed in Cordoba, Argentina on Monday last week, then tried to travel to neighboring Uruguay, but was denied entry and returned to Ezeiza outside Buenos Aires.
The crew also included 14 Venezuelans, who were free to go.
‘Propaganda’
Iran said Monday Argentina’s move was part of a “propaganda” campaign against Tehran amid tensions with Western countries over negotiations to revive a 2015 nuclear deal.
The grounding of the Emtrasur plane came days before Venezuelan President Nicolas Maduro visited Tehran on Saturday for the allies, both subject to US sanctions, to sign a 20-year cooperation pact.
Iran’s foreign ministry spokesman Saeed Khatibzadeh told reporters the grounding of the plane was part of efforts seeking to “cause a feeling of insecurity.”
The plane was sold by Iran’s Mahan Air to a Venezuelan company last year, he said.
Mahan Air is accused by the United States of links with Iran’s Revolutionary Guards.
“These recent weeks are filled with propaganda, are full of psychological operations, these wars of words that want to infiltrate the minds and composure of the people… this news is one of those,” said Khatibzadeh.
Monday’s court ruling to hold the crew’s passports came after a successful bid by the DAIA organization that represents Argentina’s Jewish community to be listed as a plaintiff in the investigation.
Interpol has arrest warrants out for former Iranian leaders suspected of involvement in an attack on a Jewish center in Buenos Aires in 1994 that killed 85 people and injured hundreds.
It remains the deadliest terror attack in the country with South America’s largest Jewish population.
The grounding of the plane came as a resolution was adopted by the International Atomic Energy Agency’s Board of Governors to censure Iran.
Talks in Vienna, under way since April last year, aim to return the US to a nuclear deal known as the Joint Comprehensive Plan of Action (JCPOA) that it left in 2018.
The deal had given Iran sanctions relief in exchange for curbs on its nuclear program to guarantee that it could not develop a nuclear weapon something Tehran has always denied wanting to do.
Iran said Monday that all measures it has taken to roll back on its commitments under the deal are “reversible”.