New York counterterror police said they were investigating on Saturday after a man threw "ignited devices" near far-right protesters demonstrating outside the mayor's home.
NYPD Commissioner Jessica Tisch said the devices contained nuts, bolts and screws as well as a fuse -- but it was not yet clear if they were functional improvised explosive devices, or hoax imitations.
The FBI New York said in an X post that its Joint Terrorism Task Force was "actively investigating", along with New York City Police.
There was no indication the incident was related to the ongoing hostilities in Iran, Tisch added. Police arrested six people over unrest at the protest, she said, including two suspects in connection with the devices.
Far-right influencer Jake Lang was demonstrating against alleged "Islamification" and calling for an end to "public Muslim prayer" in New York in front of Gracie Mansion, the residence of mayor Zohran Mamdani, who is Muslim.
His protest drew around 20 people, police said, while counterprotesters numbered about 125.
A man wearing a dark hooded sweatshirt and beige cargo pants was handed a device wrapped in tape and billowing smoke by a fellow activist. He dropped it near a line of police before vaulting a crash barrier.
The man also threw a similar device near Lang's group of protesters.
"Witnesses reported seeing flames and smoke as it travelled through the air before it struck a barrier a few feet from police officers," Tisch told a briefing, naming the suspect as Amir Balat, 18.
"Mr Balat then... gets a second device from a man.
"Mr Balat lights the device and starts running with it. He then drops the device."
Moments later, he and the other man were detained by police, who were heavily deployed to the protest.
- 'An idiot' -
"The bomb squad responded and... based on a preliminary examination and X-ray imaging, the devices which were a bit smaller than a football appeared to be a jar wrapped in black tape -- importantly with nuts, bolts and screws along with a hobby fuse that could be lit," Tisch added.
"We don't yet know if they contained energetic (explosive) material."
The man, apparently a counterdemonstrator opposed to Lang, shouted "Allahu akbar" ("God is the greatest"), an AFP correspondent at the scene heard.
A demonstrator opposed to Lang, teacher Mia Kurzer, 23, told AFP she "showed up because we have to show that hate has no place in our city."
"We democratically elected a mayor who is Muslim -- and that's New York. We have different cultures, and we have to celebrate those cultures."
She added that "I think (Lang) is an idiot. I think he underestimates the power of the people."
There were some scuffles, apparently between protesters and counterdemonstrators.
Police arrested six people, Tisch said, including a protester in Lang's group who used pepper spray against counter-protesters, the two men who handled and threw devices and three others for disorderly conduct and obstructing traffic.
Tisch said she did not believe mayor Mamdani was home.
Wally Khan, another protester opposed to Lang, told AFP "this is very in line with what he does from city to city. He tried to burn a Quran in ... Dearborn" Michigan.