Mr Matar’s lawyer, Nathaniel Barone, told the BBC his client plans to plead not guilty to the new charges.
“We plan on zealously and feverishly defending him on these matters,” Mr Barone said, adding that his client maintains his innocence on all the charges brought against him.
He has been held without bail since the attack.
The indictment said Mr Matar attempted to provide “material support and resources” to Hezbollah, knowing it was a terrorist organization, but the document did not detail what evidence connected him to the group.
Hezbollah is designated a terrorist organisation by Western states, Israel, Gulf Arab countries and the Arab League.
It remains unclear exactly why the 26-year-old New Jersey resident attacked the famed British author, though he told, external the New York Post, in an interview from jail, that he had watched videos of Sir Salman on YouTube. “I don’t like people who are disingenuous like that.”
In an interview with the BBC earlier this year, Sir Salman recalled Mr Matar “sprinting up the stairs” and stabbing him 12 times.
“I couldn’t have fought him,” he said of the attack that lasted 27 seconds. “I couldn’t have run away from him.”
The attack left him in hospital for six weeks recovering from his injuries.
Sir Salman’s memoir about the incident “Knife: Meditations After an Attempted Murder” was released earlier this year.
