Four Kenyans were killed in a gunfight on Tuesday between police and al Shabaab militants in Garissa, police said.
A teacher and a child were among the dead, police spokesman Charles Owino said.
“Officers manning the mast and the base together with special forces were able to repulse them,” police said.
Officers killed two attackers and recovered two assault rifles and bomb-making materials, he added.
The United States has sent more troops to Kenya to reinforce security after al Shabaab killed three Americans on Sunday in an attack a military base in Kenya used by U.S. forces.
In the latest incident, police said militants fired at a mast belonging to Safaricom and at police guarding the facility.
The attackers did not damage the telecom network, police said.
Kenya sent its troops into Somalia in 2011 after a series of cross-border attacks and kidnappings.
The Kenyan troops were later absorbed into an African Union peacekeeping force, now 21,000-strong, which supports the shaky, Western-backed Somali government.
al Shabaab has waged an insurgency in Somalia since 2008, aiming to topple the government and impose its own strict interpretation of Sharia law.
On Sunday, al Shabaab destroyed six aircraft and killed three Americans during the attack on Camp Simba in coastal Lamu country.
Four days earlier, the insurgents had killed three civilians on a bus in the same county.