Security concerns are plaguing the United States on Monday after bombings rocked New York and New Jersey over the weekend in what officials linked to act of terrorism.

The New York City Police Department released a photograph of a 28-year-old Afghanistan-born American wanted for questioning in connection with both the blast that injured 29 people in the bustling Manhattan neighborhood of Chelsea Saturday night and the pipe bombing earlier that day in Seaside Park, New Jersey.

Ahmad Khan Rahami, a naturalized US citizen from Afghanistan with an address in Elizabeth, New Jersey, was taken into custody after a shoot-out with police, local police said, more than two hours after the release of his photo.

The attacks, occurred just days after the 15th anniversary of the Sept. 11 attacks on the United States, sparked fears among the population of more than 8 million in New York City.

At 7:55 a.m. on Monday, residents in the US financial capital were alarmed with an emergency alert urging them to contact authorities if they see Rahami or have any information about him.

The klaxon-like alarm that usually sounded for flash flood warnings was sent to New Yorkers' cell phones, in a sign of the urgency authorities felt in chasing down the suspect and preventing additional bombings.

The bombings put enormous pressure on the city's law enforcement as world leaders are gathering this week at the United Nations headquarters for the annual General Assembly meeting and a UN high-level meeting to address large movements of refugees and migrants.

About 135 heads of state or government are expected to attend this week's event at the United Nations.

"We're going to have more security personnel than ever assembled over this next week during the UN General Assembly," New York Governor Andrew Cuomo said in interviews with CNN on Monday morning.

City authorities said they had bolstered an already heavy security force with 1,000 more uniformed police officers and National Guard members.

Rahami should be considered "armed and dangerous," New York City Mayor Bill de Blasio said in one of a series of TV appearances minutes after the release of the photo.

Early Monday, FBI agents flocked to an apartment above a fried chicken restaurant in Elizabeth that the authorities said was tied to Rahami.

Just hours earlier, one of the five explosive devices discovered Sunday night at the nearby Elizabeth train station exploded when investigators were trying to defuse it with a robot.

Rahami, whose fingerprint was found on an unexploded device, was manhunted in connection with the blasts that provoked suspicions of a local terror cell, according to federal officials.

In addition to the Chelsea blast on Saturday night, another unexploded device apparently made out of a pressure cooker was found several blocks away.

On the immediate heels of the blast, both New York city mayor de Blasio and New York Governor Andrew Cuomo were cautious about linking the attacks to international terrorism.

However, both struck a different tone on Monday morning.

"I suspect there may be a foreign connection," Cuomo told CBS News. "That's what we are hearing today, as the investigation goes on."

On Saturday, a pipe bomb exploded in a garbage pail along the route of a five-km charity run sponsored by the US Marine in New Jersey's Seaside Park, the Ocean County, about 129 km south of New York City.

The explosive device went off before the road run, thus inflicting no injuries or damages, according to local authorities.

Also on Saturday, a man stabbed and injured nine people at a mall in the northern US state of Minnesota before a police officer fatally shot him.

The Islamic State militant group (ISIS) quickly claimed responsibility for the Minnesota attack.

The incident was investigated as potential acts of terrorism, but did not appear to be linked with the series of bombing attacks in New York and New Jersey, according to police.

Rahami was identified by investigators using the cellphone attached on the explosive device made out from a pressure cooker, as well as his fingerprints left on the device, according to authorities.

Rahami was wounded after exchanging fire with police officers on East Elizabeth Ave in Linden, while two police officers were also reportedly injured during the shootout.

Police had also found a suspicious package and required bomb squad and police dogs to the scene.

The investigation was still underway and it's not clear if there were other suspects involved in the bombings.

US President Barack Obama, who is now in New York City for the annual UN General Assembly, delivered his first statement since the attacks on Monday morning, commending law enforcement officers and first responders for their professionalism and quick response, and urged Americans not to "succumb to the fear."

"The threat to the United States is serious," Robert Shapiro, professor and former chair of the Department of Political Science at Columbia University, told Xinhua.

Prof. Shapiro, however, believed it was "not an existential national threat unless there might be chemical or other large-scale attacks."

"I don't think the timing is related to the UN meeting but perhaps to the US elections," he said.