Justice Department officials eager to stanch the rising tide of gun violence in America launched an effort Thursday to choke off the flow of weapons to five major cities, targeting small-level “straw” buyers of firearms later used in crimes.

At a meeting with leaders at the Bureau of Alcohol, Tobacco, Firearms and Explosives, Attorney General Merrick Garland decried “the gun violence tragedy now facing the country,” which he said affects not just the security of cities and towns, but that of law enforcement officers, too.

Later in the day, Garland traveled to Chicago to talk more about the new anti-gun-trafficking efforts. Chicago is one of five cities getting extra attention from the Justice Department, along with D.C., New York, Los Angeles and the San Francisco area.

Amid a precedent-shattering pandemic, shootings rose dramatically in most parts of the United States in 2020, with initial data showing homicides spiked by about 20 percent — the largest single-year increase since such record-keeping began last century.

Historically, violent crime levels are still far below the record highs experienced in the 1990s. But there is growing concern among politicians and police — even as the Biden administration tries to balance public safety needs with demands to hold police accountable for misconduct and reduce the law enforcement presence in some neighborhoods.

President Biden last week called for cracking down on gun dealers and illegal trafficking, while urging communities to use coronavirus relief funds and other resources to hire more police, pay overtime and invest in community policing and social programs.

Law enforcement agencies are also trying to be more visible and aggressive, hoping to counter fear over alarming incidents such as the gunfire outside Nationals Park that sparked a panicked exodus on Saturday, or the fatal shooting of a young child in the District a day earlier.

On Thursday, Garland’s deputy attorney general, Lisa Monaco, toured a mobile gun-tracing operation in the District — a tricked out Freightliner truck in which agents can quickly analyze guns recovered in crimes to try to link them to other shootings or suspects.

D.C. police detective Wayne Gerrish showed her a .45 caliber pistol recovered a day earlier at a killing in the city’s 7th police district. He fired the weapon twice into a safe receptacle to get shell casings for analysis, each time neatly catching the casing as it flew out of the side of the gun.

“We all know our job is to go after those who pull the trigger,” Monaco had told ATF officials at headquarters earlier in the day. “. . . But our job is also of course to go after the sources of those guns, the corridors that they travel in and the networks that feed those guns to the places where they are doing the most violent crime. And that is what this series of strike-force efforts is all about.”

ATF officials have long said that firearms trafficking is not typically the work of large, coordinated criminal enterprises. Instead, in small-scale operations, illicit gun dealers find individuals to buy weapons, then hand them over to be resold to criminals out of town or out of state.

Such straw purchases are illegal. But it is often difficult to prove the initial gun buyers lied on their paperwork. For that reason, officials say, many cases are not prosecuted. At a briefing Wednesday night, one ATF official compared gun traffickers to “ants marching from one place to another.”

“These are challenging prosecutions to make, and a lot of times the prosecutable crimes occur where the firearms are obtained,” said the ATF official, speaking on the condition of anonymity to discuss the new investigative and prosecutorial strategy. “And in that source area, a prosecutor may dismiss such a violation as simply a paperwork violation.”

Going forward, officials said, U.S. attorney’s offices and ATF agents will seek to prosecute more straw purchases — focusing not only on major cities, but also the neighboring towns and states that supply many of the guns used in crimes, including along the Interstate 95 corridor and in Indiana, Nevada and Arizona.

Some past attempts to crack down on the sources of illegal guns have become mired in arguments over a piece of federal law known as the Tiahrt Amendment, which bars ATF from publicly identifying the major sources of guns later used in crimes. A Justice Department official, speaking on the condition of anonymity before the official announcement, said the current version of the amendment — which gun-control groups decry as a major obstacle — would not inhibit the department’s efforts.

Garland acknowledged the impact of politics on the public debate over crime on Thursday, calling on the Senate to confirm David Chipman, the Biden administration’s pick to lead ATF. The National Rifle Association has sharply criticized Chipman, a retired career ATF official who later worked as a policy adviser for the anti-gun-violence group Giffords, as an overzealous gun-control advocate. The fate of his nomination is uncertain.

NRA spokesman Lars Dalseide said the organization “has advocated for strict enforcement of current laws against criminals for decades. And, while we welcome this Attorney General and his Department of Justice into their new realm of prosecuting straw purchasers and other criminal sources of firearms, we are skeptical that an administration so focused on attacking the rights of law-abiding gun owners will follow through on policies that actually focus on criminals.”

Meanwhile, a group of Republican senators called Thursday for legislation to support licensed gun dealers by raising prison sentences for those who steal from gun stores.

“Democrats are determined to restrict Second Amendment rights for law-abiding gun owners but haven’t taken action to hold criminals accountable,” Sen. Tom Cotton (R-Ark.) said in a statement. “Violent crime is rising and criminals, especially those who steal firearms, must face serious consequences.”

Jeff Asher, a crime analyst, said the Justice Department strategy of reducing the availability of guns “is certainly a laudable goal. But I’m guessing it’s a small step relative to the overall scale of the problem, which is clearly nationwide.”

The Biden administration “is trying to take on the historic increase in murder and gun violence. But the reality is that the federal government has limited tools to make a short-term dent, and local programs or interventions from both law enforcement and the wider community are more likely to produce more immediate results,” Asher said.

Last year’s increase in homicides “was nearly everywhere, and not just in major cities,” he noted. Overall crime fell last year, even as shootings soared, he added, suggesting that the problem of rising gun violence is likely to have very specific, tailored solutions.

Increasingly, law enforcement agencies are turning to technology to try to reduce gun violence, which is often highly concentrated in a small area or pockets of cities. Acting ATF director Marvin G. Richardson told Garland on Thursday that his agency has become “data-driven and intelligence-led.”

When Garland met with Chicago police officials later in the day, they emphasized the importance of combining shot-detection technology with camera equipment.

Garland has previously announced other measures aimed at reducing violence, including tougher scrutiny of firearms dealers, a planned detailed public study of gun-trafficking trends in America, and a crackdown on “ghost guns” — kits that allow buyers to assemble firearms without serial numbers.