Police believe the two devices that were detonated in New Jersey and New York were made by the same person, a law enforcement source told Fox News on Sunday, as authorities move forward with investigations into the incidents as well as the ISIS-backed stabbing rampage in Minnesota — separate incidents that have cemented fears the United States is still a prime terror target.

As of Sunday afternoon, officials have not said publicaly there was a common link between the two bombing incidents, according to New York City Police Commissioner James P. O’Neill.

“I am concerned,” O’Neill said during a news conference. “We have a bomb that detonated and no one apprehended.”

The trio of dangerous episodes began Saturday when a pipe bomb exploded inside a plastic garbage can in New Jersey’s Seaside Park at 9:30 a.m. Investigators eventually found several devices “wired together” that did not detonate in the same garbage can.

The blast location could have proven deadly. Officials said runners participating in a charity 5K race were expected to pass by the area around the time of the explosion – but the start of the race was delayed after an unattended backpack was discovered. As a result, no one was injured.

“We have some promising leads, but no suspects,” New Jersey Gov. Chris Christie told WABC on Sunday.

Several hours later, and just 80 miles north, a bomb detonated on West 23rd St. in Manhattan at 8:30 p.m., injuring 29. The blast appeared to originate from a construction toolbox in front of a building. A garbage can was found mangled nearby.

Authorities later found a second, unexploded device four blocks away. A law enforcement source described the device to Fox News as a pressure cooker with wiring and a cellphone attached, placed inside a plastic bag. New York Gov. Andrew Cuomo said the unexploded device and the detonated bomb were “both similar in design.” The description of the bombs bore striking similarities to the pressure cooker devices used by the terrorists who bombed the 2013 Boston Marathon.

“You have to assume from the start that terrorism is a real possibility,” Rep. Pete King, R-NY, said on “Face the Nation.” Americans “are always vulnerable to these attacks.”

O’Neill said no group or individual had claimed credit for the New York blast, though police had recovered surveillance video from both scenes and were continuing to canvass for witnesses.

An hour after the New York bomb exploded, a knife-wielding man injured nine people -- seven men and two women -- during a bloody rampage at a central Minnesota shopping center. During the assault at St. Cloud’s Crossroads Mall, the man reportedly asked at least one victim if they were Muslim and also referenced Allah. ISIS-related media on Sunday morning claimed responsibility for the attack, calling the unidentified assailant “a soldier of the Islamic State.”

The mall assault ended when the attacker was shot and killed by Jason Falconer, an off-duty cop from another jurisdiction, St. Cloud Police Chief William Blair Anderson said. Falconer shot the assailant as the man lunged at him with a knife. Mayor David Kleis said the attacker got up and was shot again three times before finally expiring.

"We are currently investigating this as a potential act of terrorism," said Richard Thornton, the special agent in charge of the FBI's Minnesota field office.

The FBI was aiding local authorities and other law enforcement agencies in all three investigations.

Fox News' Rick Leventhal contributed to this report.