(CNN) Homicides and suicides involving guns have been increasing, according to new data from the US Centers for Disease Control and Prevention , after years of declines in gun deaths.

During 2015-16, 27,394 people were killed by someone with a gun in the United States, and 44,955 used a gun to kill themselves, according to a report published Thursday in the agency's Morbidity and Mortality Weekly Report.

Researchers looked at firearm homicides and suicides from 2012-13 to 2015-16 in the 50 most populous US metropolitan areas, including Los Angeles, not far from Wednesday's mass shooting at a bar in Thousand Oaks that left 13 dead, including the suspect.

Nationally, researchers estimate that 4.4 per 100,000 people were killed by someone using a gun in 2015-16. It's a higher rate for the 50 largest metropolitan areas combined, with 4.9 people per 100,000 killed by a gun. This is an increase from 2012-13, when the national rate was 3.7 per 100,000 nationwide and 4.1 per 100,000 for major metropolitan areas.

The rates vary widely by city. For example, there's a higher chance of being killed by a gun in New Orleans than in the Providence, Rhode Island, area. About 1 in 100,000 residents was killed by a gun in Providence and Warwick combined, compared with 16.6 per 100,000 residents in New Orleans.

Nationally, homicide was the 16th-leading cause of death, the new report notes. Guns were used in 74% of those deaths. For children between the ages of 10 and 19, guns were used in even more homicides: 87%.

Men and boys were most often the victims of homicides, accounting for 85% of the firearm deaths.

For suicides, there is also a great variety between cities. Oklahoma City, for instance, saw 13.5 suicides by gun per 100,000 residents, compared with New York, Newark and Jersey City, which combined for a rate of 1.5 per 100,000.

The number of people older than 10 who are using a gun to kill themselves has increased, too. Researchers don't use statistics from gun deaths for children under 10, because those self-inflicted deaths are probably accidentals, according to the report.

Suicide is the 10th-leading cause of death for everyone over 10, with guns used in half of all those deaths. It's the second-leading cause of death for young people ages 10 to 19, with guns used in 42% of those cases.

Though the gun suicide rate for young people is notably lower than for other age groups, the report finds that those numbers are increasing.

"I rarely take care of a suicide attempt with a gun in the emergency room. The kinetic energy of a bullet is far more effective than taking pills that have a longer duration and more opportunity for intervention," said Dr. Stephen Hargarten , director of the Comprehensive Injury Center, associate dean of the Office of Global Health and a professor of emergency medicine at the Medical College of Wisconsin in Milwaukee.

Hargarten, who was not involved in the new report, said many groups are working to reduce firearm-related suicides, but it remains "such a challenging area."

The latest increase in gun-related deaths is similar to the rates seen in the 2006-07 time period, the report said. The US has the world's highest rate of gun ownership by civilians, according to research, and the highest rate of gun-related deaths among industrialized countries.

The authors of the new report note that it is "too soon to know" whether this recent increase in gun deaths represents a short-term fluctuation or the beginning of a long-term trend.

Hargarten said he hopes the US government will see an increase in gun deaths in the proper frame, "as a complex biological and sociological disease," and increase funding for research. Gun violence is the least-studied of the top 30 causes of death in the United States, a 2017 study found

Hargarten said he has seen cities, states and even major medical groups starting to spend more money on this kind of research, but he -- like many others who do research on gun violence -- feels that the federal government needs to "step it up" to figure out what is causing this problem.

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"Where is the federal government in all of this? When there are so many deaths, we need to invest in this issue now," Hargarten said. "Look what we did with HIV and AIDS when it was breaking out in the '80s and '90s. The federal government addressed it, and the complexity and the political issues, and it helped groups most at risk, by investing our resources appropriately, and it made a huge difference in that disease process. It's imperative that we do that for guns."