NEW YORK — The bomb that rocked a New York City neighborhood contained residue of an explosive often used for target practice, a federal law enforcement official said Sunday, as authorities tried to unravel who planted the device and why.

The discovery of Tannerite — used in target practice to mark a shot with a cloud of smoke and small explosion — in materials recovered from the Saturday night explosion that injured 29 people may be important as authorities probe whether the blast was connected to an unexploded pressure-cooker device found just blocks away, as well as a pipe bomb blast in a New Jersey town earlier in the day.

Tannerite is legal to purchase and can be found in many sporting goods stores.

Gov. Andrew Cuomo, touring the site of the blast in Manhattan's Chelsea neighborhood, said there didn't appear to be any link to international terrorism. He said the second device appeared “similar in design” to the first, but he did not provide details.

“We're going to be very careful and patient to get to the full truth here,” New York Mayor Bill de Blasio said Sunday. “We have more work to do to be able to say what kind of motivation was behind this. Was it a political motivation? A personal motivation? What was it? We do not know that yet.”

The bombings, coupled with a stabbing attack in Minnesota, left officials across the country scrambling to determine who was responsible for the three apparently separate incidents, which all took place in one day and sowed fears of terrorism. Each incident raised the possibility of terrorist connections, prompting federal and local law enforcement to pour major resources into determining what happened and why.

Cellphones were found at the site of both bombings, but no Tannerite residue was identified in the New Jersey bomb remnants, in which a black powder was detected, said the official, who spoke on condition of anonymity.

Authorities said the Manhattan bombing and the blast 11 hours earlier at the site of a 5K race to benefit Marines and sailors in Seaside Park, N.J., didn't appear to be connected, though they weren't ruling anything out. The New Jersey race was canceled, and no one was injured.

Officials haven't revealed any details about the makeup of the pressure-cooker device, except to say it had wires and a cellphone attached to it.

Technicians in Quantico, Va., were examining evidence from the Manhattan bombing, described by witnesses as a deafening blast that shattered storefront windows and injured bystanders with shrapnel in the mostly residential neighborhood on the city's west side. All 29 of the injured people were released from the hospital by Sunday afternoon.

“When you see the amount of damage, we really were very lucky there were no fatalities,” Cuomo said.

The explosion left many rattled in a city that a week earlier had marked the 15th anniversary of the 9/11 terrorist attacks and where a United Nations meeting to address the refugee crisis was scheduled Monday.

“People didn't know what was going on, and that's what was scary,” said Anthony Zayas, an actor who was in the Chelsea neighborhood Saturday night when the bomb went off. “You didn't know if (it) was coming from the subway beneath you, you didn't know if there were other bombs, you didn't know where to go.”

Experts said a large amount of Tannerite would be required to create a blast like the one Saturday night, as well as an accelerant or other igniter.

The bomb in Manhattan appeared to have been placed near a large dumpster in front of a building under construction, said another law enforcement official, speaking on condition of anonymity to discuss the ongoing investigation.

Homemade pressure-cooker bombs were used in the Boston Marathon attack in 2013 that killed three people and injured more than 260.

An additional 1,000 state troopers and members of the National Guard were placed at transit hubs and other points throughout New York City, and extra police officials were patrolling Manhattan, officials said.

Meanwhile, a law enforcement official said federal investigators had discounted a claim of responsibility on the social blogging service Tumblr. Investigators looked into it and didn't consider it relevant to the case, said the official, who spoke on condition of anonymity to discuss an ongoing investigation.

Anthony Stanhope, 40, a songwriter who lives a block away from the site of the bombing, said he needed more answers before he could feel safe. “It's some kind of fanaticism, I don't know exactly what it is,” he said. “But somebody has an agenda to cause trouble in this country.”

The Washington Post contributed.