As the investigation continued, police said they were looking into a second suspicious device found in the same area of Manhattan's Upper East Side on Saturday.
Two people were in custody for their alleged role in Saturday's confrontation, which unfolded during a "Stop the Islamic Takeover of New York City" event led by the far-right activist Jake Lang outside the Manhattan residence of Mayor Zohran Mamdani.
The sparsely attended event drew a far larger group of counterdemonstrators, including one person who tossed a smoking object containing nuts, bolts, screws and a "hobby fuse" into the crowd, police said.
In a social media post on Sunday, Police Commissioner Jessica Tisch said the department's bomb squad determined the object wasn't a hoax device or smoke bomb, but an "improvised explosive device that could have caused serious injury or death".
The device extinguished itself steps from police officers, Tisch noted.
The same person who threw it then received a second device from another counterprotester, which was dropped and did not appear to ignite, the commissioner said.
Charges against the two counterprotesters are still pending.
Tisch said police were working with federal prosecutors and the FBI on the case. The FBI said agents with the bureau's Joint Terrorism Task Force were participating in the investigation.
"Violence at a protest is never acceptable," Mamdani said in a statement on Sunday.
"The attempt to use an explosive device and hurt others is not only criminal, it is reprehensible and the antithesis of who we are."
Later on Sunday afternoon, police said on social media that authorities investigating Saturday's events had "identified a suspicious device in a vehicle on East End Avenue between 81st Street and 82nd Street".
Several streets were closed and "limited evacuations of buildings" were ordered as the bomb squad assessed and worked to remove the device, the post said.
Around 7pm police used a flatbed truck to remove a Honda Civic and the streets were reopened.
A person associated with Lang's protest was also arrested and charged with reckless endangerment, assault and unlawful possession of a noxious matter after allegedly macing counterdemonstrators, police said.
Lang was previously charged with assaulting an officer with a baseball bat, civil disorder and other crimes before receiving clemency as part of President Donald Trump's sweeping act of clemency for January 6 defendants last year. He recently announced that he is running for the US Senate in Florida.
Earlier this year, Lang organised a rally in Minneapolis in support of Trump's immigration crackdown, drawing an angry crowd of counterprotesters that quickly chased him away.
19°C