The suspect in Tuesday's deadly truck ramming attack in New York City has been charged with "terrorism" related counts, federal prosecutors announced.

Sayfullo Saipov allegedly drove a rented truck down a popular bicycle path, mowing down cyclists and pedestrians. Eight people were killed and 12 others injured, some remain in serious condition.

According to the charge documents, filed on Wednesday, Saipov started planning the attack one year ago and was inspired by videos posted by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS).

"Saipov was motivated to commit the attack after viewing a video in which [ISIL leader] Abu Bakr al-Baghdadi ... questioned what Muslims in the United States and elsewhere were doing to respond to the killing of Muslims in Iraq," the complaint said.

The documents added that Saipov decided to use a truck to "in order to inflict maximum damage against civilians", and that he had planned to drive to the Brooklyn Bridge "to continue to strike pedestrians".

Saipov was charged with providing materials and resources to ISIL, as well as violence and destruction of a motor vehicle.

'Follow ISIL's instructions to a T'

According to police, the 29-year-old is a legal permanent US resident, who arrived in the country from Uzbekistan in 2010.

Investigators who questioned Saipov told the prosecutors that Saipov requested to display the ISIL flag in his hospital room and that he said he "felt good about what he had done".

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Earlier on Wednesday, New York Police Department Commissioner John Miller said multiple knives and two imitation pistols were found in and around the truck used in the attack.

"He [Saipov] appears to have followed almost exactly to a 'T' the instructions that ISIS has put out in its social media channels before with instructions to their followers on how to carry out such an attack," Miller said.

No group has claimed responsibility for the attack.

Later on Wednesday, Saipov appeared in court in a wheelchair. He did not enter a plea or seek bail, according to the Associated Press.

The attack is the deadliest to have taken place in New York City since the September 11 attacks in 2001.

US President Donald Trump condemned the attack, saying the US "must not allow ISIS to return, or enter, our country".

He vowed to end the Department of State's Diversity Visa Lottery Programme, which he said Saipov entered the country through, and ordered Homeland Security to "step up [the US'] already extreme vetting programme". Both comments have been criticised by rights groups, who call them "unconstitutional".

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Among the eight people killed were five men from Argentina who had travelled to New York with four other friends to celebrate a high school reunion.

One Belgian and two Americans were also killed, police said.

According to Reuters news agency, the FBI said it had located a second Uzbek man, wanted for questioning.

New York City leaders said there are no viable threats against the city, and that the city's marathon on Sunday would go ahead as scheduled, but additional security measures would be put in place.