WASHINGTON (AFP) - Violent crime in the United States rose last year, the FBI said on Monday, reporting data that Donald Trump could use against Hillary Clinton in the presidential debate.

The FBI said that in 2015 there were 1,197,704 violent crimes, an increase of 3.9 per cent compared to the previous year.

Murder and non-negligent manslaughter increased 10.8 per cent, and firearms were involved in two-thirds of those cases, the agency said.

The figures were released hours before the hotly awaited first presidential debate between Clinton and Trump. Crime was expected to be one of the key topics addressed by the candidates for the White House.

It is one of the pet issues of Trump, who depicts himself as a tough law-and-order candidate.

Although violent crime increased last year, overall the tendency over the past 20 years has been a decline. Crime levels these days in America are far below the peak years in the 1990s.

The FBI said it collects data on the violent crimes of murder and non-negligent manslaughter, rape, robbery, and aggravated assault.

The release of the report comes as murder rates have risen in several US cities in 2015 and 2016, mainly Chicago, where authorities have reported more than 500 homicides since January. That is more than all of last year.

Experts say different factors come into play depending on the city, mainly drug trafficking, gang wars and the availability of guns.