At least 36 people were killed at a quarry at Koromey in Mandera County on Tuesday morning by Al-Shabaab militants.
All the victims were non-Muslims and most of them are said to have hailed from Chaka in Kiganjo, Nyeri County.
Some survivors have told the police that Muslims who were at the site were spared.
The victims were made to line up and most of them were shot in the head while others were beheaded.
Al-Shabaab has claimed responsibility for the attack.
Police say the victims were attacked as they were sleeping in tents at the site at around 1am.
Inspector-General of Police David Kimaiyo said that they were attacked at a quarry in Koromey, about 10 km from Mandera town.
The attack happened just four hours after three men, all armed with AK-47 rifles, attacked a club in Wajir where they shot dead one person and injured 13 others.
The masked attackers raided Ngamia Club, about 800 metres from the Wajir Police Station and shot indiscriminately at the revellers. Mr Boniface Daae was shot in the back and was later pronounced dead.
Kenya police spokesperson Zipporah Mboroki said three other victims — Kevin Ojwang, Tom Gikundi and John Muchiri — were admitted to a hospital in serious condition.
After the club attack, the gunmen raided a Kenya Power sub-station but were repulsed by the officers who were guarding the area.
The attack occurred barely a day after Wajir Governor Ahmed Abdullahi asked the public to shun tribal clashes and work with police in battling Al-Shabaab.
He said a lot of resources had already been spent on resolving clan disputes, diverting time and resources from the main insecurity problem.
He also requested the police to stop harassing local businessmen and the public regarding where they get their sugar from, instead of focusing on the fight against terrorism.
Mr Abdullahi was speaking during World AIDS Day celebrations on Monday.
State House released a statement on the Mandera and Wajir attacks Tuesday and said investigations into the two incidences had been launched
The statement by State House spokesman Manoah Esipisu indicated that a full statement would be issued later Tuesday.
“The Government sends messages of condolences to the families of those who have lost their dear ones and stands by them during this difficult time,” the statement read.
On November 22, a Nairobi-bound bus was attacked and 28 passengers were shot dead at Omar Jillo in Mandera County.
The victims were also shot in the head.