The heavily armed gang stormed the Dadajabulla Police Post on Saturday night, released suspects, injured two police officers and escaped in a police vehicle.
The militiamen, numbering more than 50, also seized five rifles and ammunition. Nine prisoners, including three suspected terrorists, escaped with the attackers in the 9pm attack.Witnesses said they suspected the militia to be members of a group calling themselves Al Shabaab.
The attack came two days after the Police Commissioner Maj-Gen Hussein Ali, assured Kenyans that all borders were safe.
The injured police officers were taken to the Dadaab District Hospital and arrangements were being made to fly them to Nairobi for further treatment.
The attack, it is believed, was prompted by the arrest of three suspected terrorists from a bus that was headed for Wajir from Garissa.
Administration Police officers had at about 4pm screened the bus and detained the three over what they termed terrorism links.This was after one suspect wearing a buibui usually worn by women was found. Their mission in the area could not be established.
A passenger in the bus said one man identified himself as a British national whenever they were stopped at roadblocks. Sources said two of the suspects were traveling as Said Haret and Hashim Saleh. It was not clear by last night what their real names were.
The officers contacted their seniors at the nearby Liboi Police Station and requested for a vehicle to transport the suspects to Garissa divisional headquarters.
A Kenyan police Land Cruiser was immediately sent to pick up the suspects. The officers in the vehicle were shocked when they arrived at the patrol base and found it surrounded by militiamen who opened fire, injuring some officers.
It is not clear how the militiamen learnt that the three had been detained, but police linked them to terrorism.
North Eastern PPO, Mr Stephen Chelimo, said arrangements were being made to bring back the police vehicle and weapons seized by the gang.The police vehicle is said to have been spotted being driven past Dobley, about 5km from the main border.
Dobley region is run by Islamist militia who are trying to take over leadership in Somalia.
The Kenyan/Somalia border is porous and a number of police officers have been killed in attacks staged by militiamen.
Somali Transitional Government has no authority and is facing a major rebellion from several Islamic militiamen.