Police commissioner Riah Phiyega expressed concern about police killings on Wednesday after an officer was shot dead in a robbery.
"He is the first SA Police Service casualty... in 2013," she said in a statement.
She believed the possession of illegal firearms was contributing to police killings.
Phiyega urged community formations to mobilise, remain vigilant and continue to supply the police with information which would help them to deal with illegal firearms.
Sergeant Molahlehi Ephraim Mokhasi, 41, was killed in a robbery in Kopanong on Tuesday.
Four gunmen robbed a shop shortly before 2pm. The police arrived while they were trying to flee, so they ran back into the shop. They re-emerged guns blazing. The sergeant was shot and died on the scene.
The robbers ran off with cash, a laptop, and a police service pistol.
Police confronted the robbers again two kilometres away.
A female constable from the Bloemfontein dog unit was wounded in the leg and hand. A third bullet struck her bullet-proof vest. Another police officer was shot in the hand.
A gunman was killed, and a second was arrested. Another gunman was arrested on Wednesday.
The two, aged 28 and 19, were expected to appear in the Bloemfontein Magistrate's Court on Thursday, on charges of murder, attempted murder and armed robbery.