UPDATE - Authorities investigating NYC blast as act of terror

UPDATES HEADLINE, LEDE TO REFLECT TERROR INVESTIGATION, ADDS TRUMP, JOHNSON GAFFES

NEW YORK (AA) – A bomb explosion that injured 29 people in New York City is being investigated as an act of terrorism, authorities said Sunday.

Senior counter-terrorism officials reportedly told a news conference call the investigation is proceeding under the theory that the bombing in the Chelsea neighborhood of Manhattan was an act of terror, but so far there has been few leads on who is responsible.

The investigation is being conducted by a joint FBI-New York Police Department task force.

New York Gov. Andrew Cuomo told reporters earlier in the day that authorities had not yet found any links to international terrorism.

"At this time there is no evidence of an international terrorism connection with this incident, but it's very, very early in the investigation," Cuomo said.

The 8.30 p.m. Saturday explosion at 131 West 23rd Street in the Chelsea neighborhood caused "significant damage" to both sides of the street, Cuomo said, adding the fact that there are no deaths was "something to give thanks for ... because when you see the damage, we were really lucky".

The cause appears to be a pressure cooker device, similar to the one used in the Boston Marathon bombings in 2013 that killed three people and injured hundreds.

Officers found another one, which did not detonate, four blocks away on the 27th Street, treated as a second site. Cuomo said both devices were "similar in design".

He said all of the injured, including one case considered serious, have been released from the hospital.

“We will find whoever did this or whatever group did this and they will be brought to justice, period,” the governor said. “We will not allow these type of people and these type of threats to disrupt our life in New York."

An additional 1,000 New York State Police officers and National Guard troops will be deployed to patrol bus terminals, airports and subway stations.

The deployment is “just to err on the side of caution," according to Cuomo. "I want New Yorkers to be confident when they go back to work on Monday that New York is up and running and we’re doing everything that we need to do."

The governor added that New York and New Jersey were cooperating and sharing resources after the Chelsea blast and a pipe bomb explosion in Seaside Park, New Jersey, earlier Saturday, which forced the cancellation of a charity run to benefit the Marines and Navy.

That blast, in which Cuomo said a different type of explosive was used, caused no casualties.

Presidential candidates had markedly different responses to the incidents.

Democratic nominee Hillary Clinton told reporters she had been briefed about the three attacks. "We need to do everything we can to support our first responders -- also to pray for the victims. We have to let this investigation unfold," she said.

Republican Presidential candidate Donald Trump offered his condolences to the Chelsea victim's families -- despite the lack of fatalities.

"I would like to express my warmest regards, best wishes and condolences to all of the families and victims of the horrible bombing in NYC," he wrote on Twitter.

And Libertarian presidential candidate Gary Johnson mistakenly said he was thankful that nobody was injured in either the Chelsea bombing, or a knife attack in Minnesota, which has since been claimed by Daesh.

It is not Johnson's first gaffe with current events. During an interview earlier this month he responded to a question about Syria's pre-war largest city by asking,: "What is Aleppo?"