In a later statement, Donald Trump said his "thoughts and prayers" were with the victims and their families, thanking the first responders who stopped the suspect and gave immediate aid to victims.
At least eight people have been killed in a vehicle attack and shooting near the 9/11 memorial site in New York.
Officials have not confirmed the name of the suspect in the New York City attack, who was shot by police and remained in critical condition Tuesday night.
Argentina's President Mauricio Macri tweeted that he was "profoundly moved by the tragic deaths this afternoon in NY. We have reached out to law enforcement to provide our full assistance", an Uber representative said in a statement.
Writing on Twitter, he said: "I am deeply saddened to announce a Belgian victim in Manhattan - I express my condolences to the family and friends".
They were Hernán Mendoza, Diego Angelini, Alejandro Pagnucco, Ariel Erlij and Hernán Ferruchi.
"The consulate general continues working in permanent contact with the police authorities and the hospital that received the affected, as well as with the relatives in Argentina".
But a planned Halloween parade went ahead as scheduled under tight security, and Governor Cuomo has vowed the city would not be cowed by the latest attack, ordering the new World Trade Center to be lit red, white and blue "in honor of freedom and democracy".
Saipov had lived in a flat complex at Tampa, near the Hillsborough River, and The Washington Post reported that on Tuesday evening plain clothes investigators were seen departing the complex.
Independent Travel Expert, Frank Brehany, told Express.co.uk: 'The incident in New York City will send a chill across continents as a reminder of events here in Europe over the last 3 years'. He also reportedly shouted "Allahu Akbar", which translates to "God is great" in Arabic, as he carried out the attack.
Records also show traffic offences for Saipov in Maryland, Pennsylvania and Missouri, according to multiple news outlets.
The German Foreign Ministry said Wednesday that a German woman was among those injured. Only days earlier, before flying to the U.S., they had posed for a group photo, all of them wearing T-shirts with the word "Libre", or Free.
He lives in the Chestnut Hill area of Newton, near Boston.
"It was simply a matter of being in the wrong place at the wrong time", Mountain said.
"He was a very happy guy", said Matkarov, who added that Saipov was married with kids and worked as a truck driver.