The four border patrol police officers were manning border point 4 when the attacker hurled a grenade at them.
Olaka further said investigations are currently underway.
The officers who were guarding the Kenya Somalia border were on their usual patrol before they were hit by the grenade.
The grenade is said to have been hurled by an assailant who sneaked into the area pretending to be a pedestrian.
Mandera town has remained relatively calm in the recent past, and has not witnessed any terror attack for two years.
Meanwhile, the government has assured Kenyans of their security during and after this festive season.
Interior Cabinet Secretary Dr. Fred Matiang’i said despite a few insecurity challenges, the ministry has taken a multi-agency approach to deal with crime countrywide.
Speaking Tuesday when he joined police officers at the Kayole Police station, Nairobi County, for Christmas celebration, Dr. Matiang’i lauded various security agencies and the public for working as a team that has led to a significant reduction of crime and decrease in road accidents in the country.
Flanked by the Inspector General of Police, Joseph Boinnet, and other senior police commanders from the county, the CS further revealed that the government has already dispatched a heavy security detail to flush out criminals terrorizing people in Kisauni, Mombasa and other coastal areas.