A man whose homemade explosive device detonated Monday morning as he walked through a tunnel at New York City's Port Authority Bus Terminal is in custody and being treated for severe burns and lacerations.

New York City police chief James O'Neill identified the 27-year-old suspect as Akayed Ullah during a press conference following the explosion. Little is known about Ullah, though when asked about reports that he had made statements in support of the Islamic State, law enforcement authorities did not directly deny it, instead acknowledging generically that he made "statements" but declining to elaborate.

The incident occurred around 7:20 a.m. ET Monday morning, inside a heavily trafficked below-ground walkway that links the Eighth Ave. subway lines running under Port Authority with the Seventh Ave. lines running under Times Square. In addition to the suspect, police said three other individuals sustained minor injuries. Two of them took themselves to a local hospital.

Ullah was allegedly found wearing "an improvised low-tech explosive device attached to his body" using velcro and zip ties.

"Let's be clear: this was an attempted terrorist attack," New York City Mayor Bill de Blasio told reporters. "At this point, we only know of this one individual who, thank God, was unsuccessful in his aims."

New York Gov. Andrew Cuomo encouraged residents of the city to be vigilant in the coming days and alert local law enforcement authorities of anything unusual inside the subway system or at various tourist attractions.

"This is New York. The reality is we are a target by many people who would like to make a statement against democracy, against freedom," Cuomo said. "Anyone can go on the Internet and download garbage and vileness on how to put together an amateur-level explosive device."

He continued, "The counter-reality is that this is New York and we all pitch together and we are a savvy people and we keep our eyes open. And that's what 'see something, say something' is all about."

Law enforcement authorities said Ullah was in custody and being treated for injuries at Manhattan's Bellevue Hospital on Monday.