A handgun seized by D.C. police in Ward 7 on Wednesday. (Courtesy of D.C. police)

Flanked by tables filled with assault rifles and long guns, the District’s mayor and police chief warned Thursday about what they called a proliferation of high-powered weapons on the streets of the nation’s capital.

Twice in the past week, Police Chief Cathy L Lanier officers seized AK-47s, one in the hands of a 17-year-old who also had 180 rounds of ammunition and had threatened to kill his girlfriend “and her entire family, and then shoot up her school.”

Lanier said cases like that and others “make you shudder.” Police said they’re seeing more and more shootouts on District streets in which “everybody is armed.”

D.C. Mayor Muriel E. Bowser joined Lanier, Del. Eleanor Holmes Norton (D-D.C.) and other officials are calling for “common-sense gun reform.” The event was intended to keep the gun issue in the District at the forefront as discussions continue in the aftermath of the massacre at a gay nightclub in Orlando. It also came the same day that House Democrats staged a sit-in in the chamber to call for a vote on gun-control measures.

Lanier has repeatedly blamed, at least in part, large-caliber weapons with large-capacity magazines, some capable of holding 50 or more bullets, for a 54 percent increase in homicides from 2014 to 2015. This year, there have been 61 homicides, down from the 63 reported at this point in 2015.

An assortment of weapons seized on D.C. streets. (Peter Hermann/The Washington Post)

On Thursday, D.C. Police Det. Wayne Gerrish showed some of the firepower spread on one of the tables. He noted that one AK-47 purchased in another state for $100 was resold in the District for $1,500. One gun had a drum magazine, similar to an old Tommy Gun, that could hold 50 bullets. Police said some of guns on the table could shoot into a crowd and the bullets would pass through several people.

“We run across these more and more often,” Gerrish told Bowser (D).

Earlier this week, police arrested three men, two from Newport News, Va., after finding a TEC-9 semiautomatic assault pistol and a .45-caliber handgun in the trunk of a parked car in Edgewood, in Northeast Washington.

Police said there were 55 bullets and two extended magazines in the vehicle.

There is no clear explanation for why there may be more high-powered weapons in the city, police have said. Lanier said that many of the guns in the District are bought legally in Maryland and Virginia.

“We know that in our city, families are torn apart every day, or certainly all too often, by gun violence,” Bowser said. “We know the residents of the District are fed up with gun violence.”

Lanier said members of the Gun Recovery Unit have seized more than 3,000 firearms since mid-2007.

Looking at the array of guns on display, the police chief said: “I hate the thought that my officers have to go out and face these weapons over and over again. For them to put their lives on the line against these guns, and sometimes the same people with new guns, is unacceptable.”