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The number of police officers murdered in the line of duty rose 89 percent in 2014, with a total of 51 cops killed across the US, up from just 27 the year before, according to preliminary annual statistics released by the FBI on Monday.

The vast majority of the police officers were killed with firearms, with 46 of the 51 deaths resulting from gunshot wounds, including "32 incidents with handguns, 11 incidents with rifles, and three incidents with shotguns," according to the FBI.

Regionally, the South saw the largest number of law enforcement officials die in the line of duty, with 17 losing their lives last year. Another 14 died in the West, along with eight in the Midwest and Northeast respectively. The remaining four officers were killed in Puerto Rico.

While the 2014 figure indicates a sharp annual increase in officer killings, on average 64 officers have been murdered each year for the last 24 years, with figures dating back to 1980.

The highest number of officers died while responding to domestic disturbance calls and conducting traffic stops, at 11 and 10 officers respectively. Eight cops were killed in ambushes. A majority of the slain law enforcement officials were wearing body armor, and most did not use their weapons during the incidents.

In terms of other law enforcement deaths, a total of 44 officers were killed accidentally while on duty, a majority of whom died in car accidents. Other causes of death included drowning, accidental shootings, and smoke inhalation. This figure was down from 49 officers in 2013.

One of the most high profile officer killings in 2014 occurred in New York City in December, when Ismaaiyl Brinsley ambushed New York City Police Department Officers Rafael Ramos and Wenjian Liu while they were seated in their parked patrol car. He shot and killed the officers after making threats against the police and and posting photos of his gun on Instagram.

Two more police officers were gunned down on Sunday in Mississippi during a routine traffic stop. Authorities have charged 29-year-old Marvin Banks and his 22-year-old girlfriend Joanie Calloway in the murder, while also slapping charges on younger brother Curtis banks for being an accessory to murder.

The FBI will release final statistics for 2014 police officer deaths later this year.