Armed men suspected to be al Shabaab militants ambushed two police vehicles heading to Arabia from Mandera town on Friday.
The attackers had planted explosive mines near Mansa, three kilometres from Arabia.
Sergeant Bishar Issack, who was driving the second car, said a gunfight followed, with the insurgents who walked about 4km from the borderline.
Issack said the shootout that lasted about 30 minutes left three soldiers with wounded.
They were taken to Lafey hospital, he said, adding he drove the damaged car to Fino.
Issack said the militants also attacked Alungu post office but were driven away by soldiers who were on duty.
Mandera county commissioner Fredrick Sishia has assigned soldiers from the GSU, RDU and Kenya Defence Force to the borderline.
The terrorists have carried out several attacks on Mandera-Lafey-Elwak road.
A bus attack resulted in the redirection of all public service vehicle to alternative routes.