New York attacker 'may have been brainwashed', says sister

The Uzbek immigrant accused of carrying out a car ramming attack in New York that killed eight people earlier this week may have been "brainwashed", his sister said.

Sayfullo Saipov, 29, was charged on Wednesday with driving a rented pickup truck down a riverside bike trail, crushing pedestrians and cyclists, in support of Islamic State group.

His sister Umida Saipov, who lives in the capital of Uzbekistan, Tashkent, has appealed to US President Donald Trump to ensure her brother receives "a fair trial", adding that her family believes he may have been brain washed. 

"We don't know who has brainwashed him," she told Radio Free Europe. "Perhaps he's become part of some organised group. I don't know, honestly, how long it will take for his head to get rid of that poison, but I'm sure he will come to his senses, God willing."

She said she hopes her brother will not be sentenced to death in a rushed show trial.

Saipov is currently in a detention facility on terrorism charges.

Eight people were killed and dozens more were injured during Tuesday's attack in Manhattan.

US President Donald Trump called on Thursday for Saipov to be executed, just as the IS group described him as one of its "soldiers". 

"Would love to send the NYC terrorist to Guantanamo but statistically that process takes much longer than going through the Federal system," Trump tweeted.

"There is also something appropriate about keeping him in the home of the horrible crime he committed. Should move fast. DEATH PENALTY!" Trump added.