After a bloody week that contributed to a steadily rising homicide rate, officials from the District and Virginia promised Thursday to aggressively prosecute the purchase and possession of illegal firearms on both sides of the river.

“Our message to those who traffic in illegal firearms is that you will be found, and you will be prosecuted to the full extent of the law,” Jessie Liu, the U.S. attorney for the District of Columbia, said at a news conference at the Bureau of Alcohol, Tobacco, Firearms and Explosives. She spoke in front of a cache of illegal firearms police said were recovered from D.C. streets.

More than 1,000 illegal guns have been found by police this year, D.C. Police Chief Peter Newsham said, and 6,000 in the past three years.

Half of the people arrested on murder charges in the District last year had a prior gun arrest, he said, adding that statistics show that current penalties are not deterring people from committing crimes.

“We must hold every gun offender accountable,” he said. “There’s not going to be any first chances on this.”

Since promising in February to start bringing more felony gun possession cases in federal court, where penalties are harsher, Liu said her office has indicted 65 such cases.

D.C. Mayor Muriel E. Bowser (D) said the D.C. Superior Court was finalizing a “red flag” law approved by the D.C. Council last year that requires police to seize weapons from people deemed a danger to themselves or to others.

The announcement came amid a spike in homicides that has rattled the District this month, with nine people killed or found dead from gunfire in five days. The victims included a father and his teenage son, each found shot in the head inside their apartment, and 11-year-old Karon Brown.

“Too many times on those scenes, there’s frequently the same question: ‘How are these guns coming into our neighborhoods? We don’t make guns in D.C. How are all of these guns on our streets?’ ” Bowser said at the news conference.

More than one-third of illegal firearms in the District come from Virginia, according to statistics from ATF.

Bowser said she was optimistic that “an intense focus on Virginia” would have an effect on gun violence in the District.

“If you purchase a firearm in Virginia for someone else or if you live in D.C. and provide a false Virginia address, we will prosecute you, and it’s a felony,” G. Zachary Terwilliger, the U.S. attorney for the Eastern District of Virginia, said at the news conference.

Although he credited his office’s “aggressive” approach on gun crimes with a 14 percent drop in homicides in Virginia last year, an effect in the District has yet to be seen.

As of Thursday afternoon, D.C. police reported 96 homicides this year, up about 10 percent from the 87 at this time in 2018.

There were 160 homicides last year, an approximately 40 percent jump from 2017’s total of 116.

More crimes are being committed and more disputes are being resolved with guns, authorities said, leading to more shootings and an increased case fatality rate.

Police said one man fatally shot a friend who made fun of his eye patch, and a road crew worker was killed after arguing with a man he had told not to cross a street. In another case, they said, a man was shot and killed during an argument over practice time at a music rehearsal. Authorities said Karon was shot by an adult as he tried to flee a fight involving other people outside a McDonald’s in Southeast Washington.

“A petty argument or disagreement occurs, or someone feels disrespected, and rather than moving on, a readily available gun is introduced and someone ends up seriously injured or killed,” Newsham said Thursday.