Homicides in the United States went up by more than 10 percent in 2015 over the year before, while violent crime increased by nearly 4 percent in the same period, according to new statistics released Monday by the FBI.

All told, the country reported its highest estimated violent crime rate in three years, and while these numbers are far below those seen one or two decades earlier, they mark a sharp increase following two years of declines, the FBI’s summary of crime figures showed.

The long-awaited FBI report was released amid heightened scrutiny of violent crime in the United States, propelled by an increase in homicides in a number of major cities and repeated comments from Republican presidential candidate Donald Trump.

“The report shows that there was an overall increase in violent crime last year, making clear what each of us already knows: that we still have so much work to do,” Attorney General Loretta E. Lynch said Monday in Little Rock. “Violent crime endangers lives, destroys families and paralyzes neighborhoods … In some ways, violence affects all of us — and so all of us have a responsibility to end it.”

As if to emphasize her point, while Lynch was making her remarks, officials in Houston were responding to an active shooting scene that wounded at least nine people before the gunman was killed.

While the FBI released its statistics on 2015 nearly 10 months after the year ended, a debate over crime has been raging based on the number of cities where homicides have gone up and, in some cases, surged dramatically. Police departments in many of the places that saw homicides go up in 2015 say they have also seen increases so far this year, though officials and experts have disagreed on precise causes.

FBI Director James B. Comey has been among the most high-profile figures voicing concerns, and he said earlier this year that he remains worried because homicides continue to spike in major cities nationwide so far this year.

“I don’t know what the answer is, but holy cow, do we have a problem,” Comey said to reporters in May. He acknowledged that this comes at a time when crime is far lower than what it was during the late 1980s and early 1990s, but he said this is little comfort.

“Something people say to me, ‘Well, the increases are off of historic lows,’ ” Comey said then. “How does that make any of us feel any better? I mean, a whole lot more people are dying this year than last year, and last year than the year before, and I don’t know why for sure.”

Americans are generally worried that crime is going up nationwide, though Gallup polling dating back nearly three decades shows that Americans almost always think crime is going up, even when it is significantly declining.

Still, nationwide crime numbers have gotten more attention recently, and two dozen police agencies say they have seen more killings this year than the same point last year.

In an analysis last week, the Brennan Center for Justice, a law and policy institute, found that Chicago has accounted for a remarkable share of the increase in homicides nationwide among big cities, just as it found that Chicago, Washington and Baltimore saw most of that increase in 2015.

Lynch, in her remarks Monday, sought to put the new FBI report in a historical context, noting that while violence spiked in some areas, this was not uniform or at unprecedented levels.

“But the report also reminds us of the progress that we are making,” Lynch said. “It shows that in many communities, crime has remained stable or even decreased from the historic lows reported in 2014. And it is important to remember that while crime did increase overall last year, 2015 still represented the third-lowest year for violent crime in the past two decades.”

As Lynch and other experts note, the crime numbers — while rising — do not reach the levels seen decades ago.

In 2015, there were an estimated 372.6 violent crimes per 100,000 residents; in 1995, there were an estimated 685 violent crimes per 100,000 residents, according to the FBI’s data. The total 1.197 million violent crimes last year was the highest raw number since 2012, but it trails the 1.798 million seen in 1995, when the United States had more than 50 million fewer residents.

Last year, the murder rate was 4.9 per 100,000 residents, down from 8 per 100,000 residents in 1995.

There were also incredible differences between parts of the country, as the violent crime and murder rates in the South far outpaced those in the other regions. The FBI notes that the South is the country’s most populous area, but notes that 45 percent — nearly half of all murders — occurred in that region alone.

Once again, white people were far more likely to be killed by white people and black people far more likely to be killed by black people. One in five people were killed by an acquaintance, the FBI found, and almost half of all killings involved a single victim and offender, the FBI found. Nearly 1 in 10 people killed in murders were younger than 18; more than 400 murder victims were younger than 5.

These FBI’s figures are released through its Uniform Crime Reporting Program, which collects numbers from more than 18,000 law enforcement agencies participating voluntarily. In addition to the crime figures, the FBI also collects data about how often police officers fatally shoot people, but these numbers are incomplete because of the voluntary reporting. For example, the data released Monday shows that 441 people were fatally shot by law enforcement officers last year in cases deemed justifiable homicides, while The Post’s database (launched in part because of incomplete federal data) found that 990 people were fatally shot by officers.

In preliminary statistics released in January, the FBI reported that over the first half of 2015, violent crime was up over the same period in 2014, with more murders, rapes, assaults and robberies. For the entire year, the FBI found that along with an uptick in violent crime and murders, the country also saw more rapes, robberies and aggravated assaults in 2015 than the previous year, while property crimes, burglaries and larcenies fell.

Among all of the violent crimes reported last year, guns were part of a sizable percentage, the FBI found. Guns were used in more than 7 in 10 murders, more than 4 in 10 robberies and a quarter of all aggravated assaults.

The FBI statistics were released just hours before Trump and Hillary Clinton, his Democratic opponent, meet for their first presidential debate. Crime and law enforcement have become major themes of this campaign, with Trump framing himself as a candidate of law and order and regularly invoking increases in homicides (particularly in Chicago, which led the country in killings last year and far outpaces any other city so far this year).

Trump’s comments on the subject, part of a campaign pitch that describes America in grim, bleak terms, have ranged from accurately citing statistics showing homicide increases in cities to blanket, untrue assertions that crime is at unprecedented levels. The Brennan Center, in its analysis last week, said there is no proof of a nationwide crime wave.

“The numbers do indicate murder has increased in a small number of cities around the country, which must be addressed immediately,” Ronal Serpas, a former police chief in New Orleans and chairman of Law Enforcement Leaders to Reduce Crime and Incarceration, a group organized by the Brennan Center, said in a statement. “Evidence shows that focusing police resources on combating local violence would help. But, false narratives about rising crime distract lawmakers and the public.”

Last year, the FBI found that the estimated number of violent crimes fell in 2014, just as it did in 2013, falling very slightly from a year earlier. FBI data show, and criminologists and experts emphasize, that even though violent crime and homicides may be increasing over recent years, they still lag behind what this country saw amid the bloodshed of a quarter-century ago.

Law enforcement officials and criminologists have differed on what may be causing the increase in homicides, saying that it could stem from gang violence or drug sales and addictions.

The recent increases in crime come amid intense scrutiny on police officers and how they use deadly force, an issue that emerged as a central national debate after an officer fatally shot a teenager in Ferguson, Mo., in 2014. Since then, protests has continued to crop up in cities nationwide, most recently in Charlotte, which just days ago saw violent demonstrations erupt after an officer fatally shot a man there.

This intense focus on how law enforcement uses force has caused many officers to say they feel like they are under attack, a sentiment that flared up again after a three-day span in July that saw deadly shootings of and by police officers. Comey has been among those questioning whether this increased scrutiny has played a role in the uptick in violence, asking whether it is occurring because officers are pulling back due to the negative attention. This theory is known as the “Ferguson Effect,” and in a report released this summer, criminologist Richard Rosenfeld said he believes there is a connection between the crime levels and criticism of police.

“We need more transparency and accountability in law enforcement,” Comey said in a statement accompanying the report’s release Monday. “We also need better, more informed conversations about crime and policing in this country.”

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This story, first published at 11:34 a.m., has been updated.