2016 was the most dangerous year for law enforcement in five years, according to a new report.

On Monday — the beginning of National Police Week — the Brady Campaign to Prevent Gun Violence released a report showing 135 law enforcement officers were killed in 2016. This number was the highest since 2011 and a 56 percent uptick from 2015.

As of the report's release, 15 law enforcement officers have been shot and killed so far in 2017.

The Brady Campaign found that the number one cause of death for these individuals in 2016 was guns, and the year saw a 500 percent increase in police killed with rifles from 2015 to 2016.

2016 also had the highest number of ambush-style shootings of police in more than two decades, including the shootings of five officers in Dallas, Texas, in July, and three more in Baton Rouge, La., less than two weeks later.

The report also revealed that 53 percent fewer police officers were shot and killed in the line of duty in the 19 states (and the District of Columbia) that require a background check on all handgun sales.

President Trump told families of fallen police officers on Monday on Capitol Hill, "You do not grieve alone." Monday is National Peace Officers Memorial Day.