New York City mayor Michael Bloomberg, police commissioner Raymond Kelly, and other officials hold a news conference with seized guns at the police headquarters in New York August 19, 2013. Officials announced that they seized more than 200 guns in the city's largest ever bust. Eric Thayer/Reuters

Walker and Campbell were arrested earlier this month by local police in their home states, authorities said. The names of their defense attorneys were not immediately available.

The alleged smugglers, Walter Walker and Earl Campbell, were among 19 people arrested in New York, and North Carolina and South Carolina - states where the guns originated - as the result of a 10-month investigation. Also charged was an aspiring rapper from Brooklyn.

Two smuggling rings were alleged to have acquired guns that had been stolen or purchased illegally in North Carolina and South Carolina, taking advantage of a premium on guns in New York due to stricter gun-control laws, New York City Special Narcotics Prosecutor Bridget Brennan told reporters.

"There is no doubt that the seizure of these guns has saved lives," New York Mayor Michael Bloomberg told a news conference, using the opportunity to defend the New York Police Department's controversial "stop and frisk" tactic, which a U.S. judge last week ruled unconstitutional.

New York City authorities reported Monday the largest gun seizure in city history, capturing 254 weapons and arresting 19 people from smuggling rings that are accused of running guns northward from the Carolinas.

'Iron pipeline'

For years, Bloomberg and NYPD Commissioner Ray Kelly have decried what is known in law-enforcement circles as the "iron pipeline" - a gun smuggling route on the U.S. East Coast, moving guns from states with more lax firearms laws, such as those in North Carolina and South Carolina, up to New York and other Northeast states, where black-market guns fetch at least three times their retail price.

New York has some of the nation's strictest gun-control measures and a mayor who has crusaded for tougher laws in other states.

Wiretap evidence showed that sellers in the Carolinas knew the weapons were destined for New York, according to Brennan.

"Perhaps the two most disturbing aspects of the gun-trafficking operation were the simplicity of the business model, and the complete indifference of the gun suppliers to the mayhem their actions would cause here in New York City," Brennan said.

The gun case was a spinoff of a drug investigation in Brooklyn that turned up Instagram photos of handguns and wads of cash posted by the rapper. Wiretap and other evidence led investigators to Walker, 29, of Sanford, N.C. and Campbell, 24, of Rock Hill, S.C., who were smuggling guns separately but using the same middleman in New York City, authorities said.

The two tapped a loose network of suppliers in their hometowns, authorities said. Some guns were obtained on the black market, while others were bought from gun dealers using straw buyers to get around one-gun-a-month restrictions.

"The problem is that the gun laws passed now, so it's like now I can only buy a gun from a gun store every 30 days," Campbell complained in one conversation, according to an indictment. "So I had to, like, pay different people to keep buying different guns."

Before heading to New York, Campbell would get photos of the guns his suppliers were offering and send the images to the undercover officer, authorities said. Both defendants would travel to the city carrying a dozen or more handguns, rifles and shotguns in bags that were stowed in luggage compartments of Chinatown-based carriers also favored by drug couriers, investigators said.

One of the discount bus companies charges $60 one-way from Raleigh, N.C., to New York. The fare is about half that charged by Greyhound, which, unlike the Chinatown buses, requires identification for boarding.

Walker met two times last year with the middleman and the undercover officer at the rapper's Brooklyn recording studio to sell the undercover firearms, the indictment said. He also allegedly sold weapons to the undercover in April in Manhattan.

In January, the undercover officer met with Campbell and his girlfriend, who was carrying assault rifle parts in her zebra-striped suitcase, authorities said. The girlfriend struggled to assemble the weapon in the backseat of a car by using a YouTube instructional video she called up on her smartphone, investigators said. When she failed, the undercover bought the pieces anyway for $1,100, they said.

According to Kelly, Campbell shifted sales from Brooklyn to Manhattan earlier this year out of fear of being caught up in the NYPD's "stop and frisk" police stops in the Brownsville section of Brooklyn, one of the city's high-crime neighborhoods.

"I can't take them [guns] to my house ... 'cause I'm in Brownsville," Kelly quoted Campbell as saying in a January phone call captured on a wiretap. "We got, like, whatchamacallit, stop and frisk."

A U.S. district judge last week ruled "stop and frisk" unconstitutional for unfairly targeting of minorities and ordered changes to the tactic. The city has appealed the ruling, saying the practice has helped reduce crime by 30 percent.

Al Jazeera and wire services