Democratic presidential nominee Hillary Clinton issued a statement saying she strongly condemns what she characterised as "apparent terrorist attacks" in Minnesota, New Jersey and New York.
"Law enforcement officials are working to identify who was behind the attacks in New York and New Jersey, and we should give them the support they need to finish the job and bring those responsible to justice," Clinton said, adding: "We will not rest until that happens."
The former Secretary of State noted that Isis (Islamic State) had asserted responsibility for the stabbings of nine people inside a shopping centre in St Cloud, Minnesota, about 110km northwest of Minneapolis.
"This should steel our resolve to protect our country and defeat Isis and other terrorist groups," Clinton said. "I have laid out a comprehensive plan to do that."
Clinton's statement followed remarks to reporters on her campaign plane on Sunday in which she cautioned against rushing to conclusions about the attacks and criticised her Republican opponent, Donald Trump, for quickly telling an audience that an explosion in New York was a bomb that served as a reminder for the United States to "get very tough".
Today, New York Governor Andrew Cuomo, said there was "no evidence of an international terrorism connection" to the incident in the Chelsea neighbourhood of Manhattan, where an "intentional" blast apparently was caused by an improvised explosive device on Sunday. But Cuomo said "a bomb exploding in New York is obviously an act of terrorism".
In her statement, Clinton said her plan to combat terrorism "includes launching an intelligence surge to help identify and thwart attacks before they can be carried out, and to spot lone-wolf attackers."
"We also need to work with Silicon Valley to counter propaganda and recruitment efforts online," she said. "Americans have faced threats before, and our resilience in the face of them only makes us stronger. I am confident we will once again choose resolve over fear."
Yesterday, Republican nominee Donald Trump appeared to pre-empt New York City officials when he declared that a "bomb went off" in New York City before officials had released details.
Trump made the comments around 9.10 pm, shortly after the explosion in Manhattan's crowded Chelsea neighbourhood and as emergency officials were responding to the blast.
"I must tell you that just before I got off the plane, a bomb went off in New York and nobody knows exactly what's going on," Trump said.
"It's a terrible thing that's going on in our world, in our country," he added, "and we are going to get tough and smart and vigilant. . . . We'll see what it is. We'll see what it is."
Trump surrogate New Jersey Governor Chris Christie defended Trump's comments.
"Well, listen, I don't think you have to defer when saying that there was an explosion and a bomb in New York," Christie said. "I mean, everybody knew that, and it was being reported on television. . . . So there's a difference. Now, you shouldn't attribute it to any particular organisation or group if you don't have the facts or information to do that. But I think that what Donald did was perfectly appropriate."
Christie said that he does not know who is responsible for the bombings in New York and New Jersey, but he does know what to call the attacks.
"You can call them whatever you want - they are terrorism, though," Christie said on CNN. "There's no doubt about that. They're terrorism. Now, who's responsible and what the motive was is something else that, hopefully, we're going to find out in the days ahead."
Republican running-mate Governor Mike Pence says "we're all troubled in our hearts" about explosions in New Jersey and New York and a knife attack in Minnesota. Pence says that whether the incidents were acts of terrorism or inspired by terrorists, "prayer and vigilance is the order of the day".