Three suspected Al-Shabaab militants died in Fafi, Garissa County, on Friday when the Improvised Explosive Device (IED) they were assembling exploded.
Four suspected militants were injured in the incident said to have taken place at around 4pm in Kashini.
A police report seen by the Nation says the injured were picked up by people in a Toyota Hilux Double Cab vehicle with a Somalia registration number.
"The vehicle left the Santaro Al-Shabaab base in Somalia to pick up the injured and ferry them [back] for medication," the report said.
Several such incidents have taken place in parts of the country including Mandera and Lamu.
The insurgents have been planting explosives on roads, the targets being police officers who patrol terror prone areas.
The militants continue to unleash terror this year, killing more than 20 people between January and February in the North Eastern and Coast regions.
Following the attacks, the government launched an operation that culminated in freezing the accounts of the terror group's suspected financiers.
On September 2, Interior Cabinet Secretary Fred Matiang'i ordered seizure of assets and freezing of the accounts of nine individuals said to support terror activities in the region.
They were identified as Halima Adan Ali, Waleed Ahmed Zein, Sheikh Guyo Gorsa Boru, Mohammed Abdi Ali (Abu Fidaa), Nuseiba Mohammed Haji, Abdimajit Adan Hassan, Mohammed Ali Abdi, Muktar Ibrahim Ali and Mire Abdullahi Elmi.