Story highlights

Deaths are up 37% through June 15

Traffic accidents are the leading cause of death

Gun-related fatalities are up significantly

CNN  — 

About 40% more law enforcement officers have died on duty in the first five and a half months of 2014 than in the same period a year ago, the National Law Enforcement Officers Memorial Fund said Sunday.

Of the 63 fatalities through June 15, 23 were gun-related, the organization said.

There was a 53% rise in firearm-related deaths and a 37% upward trend overall, according to the nonprofit organization, based in Washington.

So far this year, traffic accidents are blamed for 25 deaths.

The increase comes after two years of declines, including 2013, which saw the lowest number of deaths on duty – 111 – since 1959.

The organization said its research team compiles the list of fatalities, which also includes job-related illnesses such as heart attacks, falls and other types of accidents.

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CNN’s Carma Hassan contributed to this report.