Federal investigators are examining a possible terrorism connection after two men threw improvised explosive devices during protests outside Gracie Mansion over the weekend, with one suspect making direct references to ISIS, according to multiple sources familiar with the investigation.

Mayor Zohran Mamdani and NYPD Commissioner Jessica Tisch plan to provide an update on the case Monday morning as the FBI joins local authorities in the investigation.

The incident occurred Saturday during dueling demonstrations outside the mayor’s official residence on Manhattan’s Upper East Side. An anti-Islam protest led by conservative influencer Jake Lang drew a much larger group of counterprotesters to the scene.

Police arrested two Pennsylvania residents, identified by Tisch as Emir Balat, 18, and Ibrahim Kayumi, 19. According to investigators, one suspect referenced ISIS in statements to law enforcement, prompting authorities to examine the incident as a potential act of terrorism.

The NYPD Bomb Squad’s preliminary analysis determined one device was not a hoax or smoke bomb but “an improvised explosive device that could have caused serious injury or death,” Tisch said in a social media post Sunday. Police officials say the device could have caused grave injury or death had it exploded as intended.

The confrontation escalated around 12:30 p.m. Saturday when the 18-year-old counterprotester “lit and threw an ignited device toward the protest area,” according to Tisch. Witnesses reported the device was smoking but extinguished itself after hitting a barrier and landing several feet from police.

The same suspect then grabbed a second device from the 19-year-old man and ignited that one before dropping it, police said. No injuries resulted from either device.

Mamdani and first lady Rama Duwaji, who are Muslim, were home during the incident. The mayor condemned the action in a statement Sunday.

The protest targeted by the counterprotesters was called “Stop the Islamic Takeover of New York City, Stop New York City Public Muslim Prayer,” according to police.

Police initially separated the opposing groups with barriers before tensions escalated. The two suspects were among six people arrested during Saturday’s demonstrations. The others included one person for deploying pepper spray and three others for disorderly conduct and obstructing traffic, according to Tisch.

The NYPD and FBI continue interviewing the two main suspects. It remains unclear whether they have retained attorneys.

Investigators are conducting ongoing tests on the second device recovered from the scene. The FBI’s involvement signals the serious nature of the investigation as authorities work to determine whether the incident meets federal terrorism criteria.

The case highlights growing tensions around religious demonstrations in New York City. Gracie Mansion, located in Carl Schurz Park on the Upper East Side, serves as the official residence of the city’s mayor and has been the site of various protests throughout different administrations.

The preliminary bomb analysis represents a significant development in what initially appeared to be a protest disturbance but has evolved into a federal terrorism investigation. The suspects’ apparent travel from Pennsylvania to participate in the demonstration adds another layer to the investigation.

Monday’s press conference is expected to provide additional details about the devices, the suspects’ backgrounds, and the ongoing federal investigation. The incident marks one of the most serious security threats at the mayor’s residence in recent years.