South African police say 51 officers were killed in the first half of 2006: a "sharp increase" on figures for the equivalent period last year.
Police chief Jackie Selebi is worried about the rise
The national police chief said the news was a source of "deep concern".
The figures were released on Tuesday, the same day that another officer was shot dead in Soweto, Johannesburg.
In the worst incident this year, four police died in a shootout in central Johannesburg last month as they tried to arrest suspects after a robbery.
"There has obviously been a sharp increase in police murders during the first six months of this year compared with the first six months of last year, which is a cause of deep concern to the South African Police Service," National Police Commissioner Jackie Selebi said.
Police spokeswoman Supt Sally de Beer pointed out that the latter half of 2005 had also seen a rise in the killing of police both on and off duty, bringing last year's total to 91.
"We will work towards ensuring a decrease over the rest of this year," she told the BBC News website.
Training programmes would make officers aware of the need to wear bullet-proof vests and not to try to tackle armed criminals alone, Supt de Beer said.
She said Johannesburg accounted for most of the police killings in the first half of the year with 23 officers dying - 16 of them while on duty.
Those killed off duty included some who were "targeted because they were known to be police in their communities," Supt de Beer said.