"A bomb exploding in New York is obviously an act of terrorism," Gov. Andrew Cuomo said in a news conference. "A bomb going off is generically a terrorist activity. That's how we'll consider it. And that's how we will prosecute it."
The New York Joint Terrorism Task Force is investigating the explosion as a possible terrorist act. Meanwhile, an explosion in a trash can near a Marine Corps charity race
route in New Jersey earlier Saturday is also being investigated by the Joint Terrorism Task Force there as possible terrorism. And the Minnesota FBI said it is investigating Saturday's knife attack in St. Cloud
as a possible terrorist act.
But in New York, law enforcement officials and the city's mayor cautioned that without a known motive, it's too soon to call the bombing there a terror attack.
New York Mayor Bill de Blasio called Saturday night's explosion an "intentional" act. But, he stopped short of calling it terrorism in the absence of evidence tying it to known terror groups.
"There's no specific and credible threat against New York City at this time from any terror organization," he said in a Saturday news conference.
He reaffirmed that point on Sunday when pressed on whether he was comfortable calling it an act of terrorism.
"Here is what we know: It was intentional. It was a violent act. It was certainly a criminal act. It was a bombing. That's what we know. To understand any specific motivation, political motivations, any connection to an organization, that's what we don't know."
Police Commissioner James O'Neill echoed the sentiment. If and when the investigation reveals a motive pointing to terrorism, "we'll say it loud and clear," he said.
"If it is an act of terrorism, we're going to come out and say it."
CNN law enforcement analyst Tom Fuentes said the very nature of the attack, the intentional targeting of a large group of people, suggested an act of terrorism.
"Whether it's domestic terrorism or international, we don't know, but it certainly would have an appearance that somebody made an attempt to kill people, on purpose."
Even so, politicians and law enforcement have a responsibility to refrain from using such language until the facts are in, said CNN national security analyst Juliette Kayyem.
It's too soon to label the blast a terror attack without knowing the motivations behind it, she said.
Terrorism is essentially a legal term describing a purposeful attack, motivated by political or ideological means, to alter politics or society through violence, Kayyem explained.
Without knowing the motivations behind the explosion it's premature to label the blast a terror attack, "unless you want to define terrorism as any violent act in an urban area," she said.
"If we start calling everything terrorism -- and in this day and age we mean ISIS -- we give credit and kudos to an organization that's willing to take it," she said.
"Let the investigation unfold. Give the NYPD space, wait for the facts. The facts will help us find the culprits and then we can decide what we're going to call them."