The toll, given by a police official speaking on condition of anonymity, was sharply higher than a count of eight dead and 12 missing given Saturday, hours after the attack blamed on local tribesmen.
"Those who were missing are all dead," the senior police officer explained.
The ambush occurred during a security operation in Kapedo, in the arid and impoverished region of Lake Turkana that is prey to regular raids and score-settlings between rival communities.
Kenya police spokesman Masound Mwinyi said late Saturday that a number of armed men had carried out the assault on the police officers early in the day.
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Last week, five people, including three police officers, were killed in another attack in the Kapedo area, according to police sources.
Diminishing water supplies and grazing areas have aggravated conflicts between communities in the area which is mainly populated by nomadic herders.
Local police are notoriously under-equipped and can find themselves outgunned because of increasing numbers of illegal firearms appearing in the area.