The police, members of an elite crowd-control unit, were returning from a night patrol in the town of Sidi Moussa, 12 miles (19km) south-east of Algiers when a group of men opened fire on them.
At least 1,700 Algerians have been killed in a wave of political violence since January 1992, when the authorities cancelled elections which the Islamic Salvation Front was poised to win.
On Tuesday suspected Muslim extremists shot dead a British computer technician in west Algeria. Malcolm Vincent, who died on his way to hospital, was the fourth foreigner killed since the clandestine Armed Islamic Group told expatriates to go home by midnight on 30 November or face sudden death. The others were a Frenchman, a Spaniard and a Russian woman.