The number of police officers "feloniously killed" in the line of duty last year sharply jumped from 2013 but was still well below the annual average for the last 3 1/2 decades, the FBI said Monday.
An average of 64 officers were killed each year from 1980 to 2014, the agency said.
The latest statistics come at a time when police training and actions have drawn national attention after the deaths of several officers, highlighting the dangers of police work.
New York residents mourned the death of Officer Brian Moore, who was slain in Queens this month. It was the third officer death in the last six months in the city.
Over the weekend, two officers were killed in Hattiesburg, Miss., after a routine traffic stop.
Despite the inherent dangers, being a police officer has been getting safer over the years, according to statistics compiled by the National Law Enforcement Officers Memorial Fund, an officer support group.
The number of annual deaths of all types was in the 200s during the 1970s and 1980s, but fell in this century to below 200 a year, the group found.
According to the FBI's preliminary statistics, 46 of the 51 deaths in 2014 involved guns: 32 were handguns, 11 were rifles and three were shotguns. Four officers were killed when vehicles were used as weapons and one officer died after being beaten.
Thirty-five of the officers were wearing body armor when they were killed, according to the statistics.
By region, 17 officers died in the South, which also had the most killings of police in 2013. Fourteen officers were killed in the West, eight in the Midwest and eight in the Northeast. Four were killed in Puerto Rico.
Police answering calls about disturbances faced the highest risk, with 11 officers dying; only one of the disturbance calls involved a domestic dispute.
Ten officers were conducting traffic pursuits or stops.
Eight officers were killed in ambushes; six of those cases were premeditated and two were during unprovoked attacks, according to the statistics.
Six officers were investigating suspicious people or circumstances.
In addition to those officers killed in felonious attacks, 44 more officers died accidentally in the line of duty in 2014, five fewer than were accidentally killed in 2013.
Twenty-eight of the officers died in automobile accidents and six in motorcycle accidents. Five were struck by vehicles and two were killed in accidental shootings. One died from blunt force trauma and one from smoke inhalation. One drowned.