Federal agents have launched a high-level investigation into an early-morning attack outside a major Manhattan government complex. Authorities stepped in after a suspect set off fireworks, ignited a blaze on the entrance steps and targeted the facility housing immigration offices.

While law enforcement quickly brought the situation under control, the targeted assault has raised serious alarm over growing tensions surrounding federal enforcement agencies.

Police took a former American soldier into custody following an alleged arson attempt on Monday outside a Lower Manhattan site housing federal immigration courts and a temporary ICE holding area.

James Barnacle, assistant director of the FBI's New York field office, confirmed that 43-year-old Andrew Arrabaca doused the area outside 26 Federal Plaza with petrol before setting it alight using a lighter and a large canister firework.

'He then pulled out an airsoft rifle and fired five to seven pellets ... in the direction of 26 Federal Plaza,' Barnacle revealed during a Monday afternoon news briefing, just hours after the attack took place.

According to Barnacle, the suspect served as a US Army missile defence mechanic from 2001 to 2005, but has since become an 'anti-American, anti-government extremist' who targeted the facility because of his intense hatred of US Immigration and Customs Enforcement.

'He had a cart; he had anti-ICE literature on it,' Barnacle said. 'When he was being arrested, he yelled derogatory terms toward ICE, used bad words.'

Social media clips of the Monday morning attack quickly went viral, showing a dark plume of smoke billowing outside 26 Federal Plaza. In addition to housing several federal offices, the building contains Manhattan's busiest immigration court and a contentious temporary ICE holding hub that has previously been condemned for cramped, unsanitary conditions.

Refusing to elaborate on Arrabaca's specific views on ICE, Barnacle pointed out that the disruption derailed a scheduled naturalisation ceremony and left a court-bound immigrant injured.

'So, that's quite unfortunate and quite ironic at the same time,' he said.

According to Barnacle, the incident also left two federal employees injured.

Addressing questions about Arrabaca's criminal past, Barnacle revealed that while he had 'a couple encounters with law enforcement that we're not ready to talk about', there was 'nothing rising to this level'.

Although his most recent address was listed in Harlem, evidence suggests he travelled by subway to Penn Station on Sunday night before sleeping rough on the street.

Beyond the airsoft rifle, Barnacle said Arrabaca was heavily armed, carrying a machete, two axes, a hammer, three fixed-blade knives and six fireworks.

'Mr. Arrabaca came armed with bad intentions,' Barnacle said. 'I will say that 26 Federal Plaza has long been a target of extremists, of terrorists, and today the extremism was brought here.'

According to Tisch, officers arrived at the scene within two minutes of the first emergency call on Monday morning. By the time NYPD units reached the building, however, federal agents had already tackled and detained Arrabaca outside the entrance.

As of Monday evening, formal charges against Arrabaca had yet to be filed. NYPD Commissioner Jessica Tisch said investigators intend to search his black Toyota RAV4, which remained parked in Harlem.

Meanwhile, New York City Mayor Zohran Mamdani described the attack on social media as 'deeply disturbing'.