A number of people were injured in the two attacks
Witnesses said heavily armed men raided a trading centre in the village of Hindi, in Lamu county, and a police station in Gamba, Tana River county, overnight on Saturday.
The Somali militant Islamist group al-Shabab said it was behind the killings.
It has made past claims it conducted various other attacks in the region.
Deputy Prime Minister William Ruto, who is currently visiting the region, is on his way to Gamba.
The nature of its attacks there is changing, with a growing use of armed units rather than grenades, improvised explosive devices and single targeted assassinations.
It would be wrong to think of al-Shabab as a purely Somali movement. Young, disaffected Muslim men, many from the Kenyan coast, provide a fertile recruiting ground.
Al-Shabab has a sophisticated propaganda machine, with radio broadcasts in the local Kiswahili language, and Kiswahili websites with instructions on how to make bombs.
Witnesses said about a dozen armed men had appeared in Hindi late on Saturday evening and opened fire.
"They went around shooting at people and villages indiscriminately," area chief Abdallah Shahasi told Reuters.
County commissioner Miiri Njenga told the agency some government offices and properties had been burned down.
All those killed were adult men apart from one teenage boy shot as he tried to flee, the AFP news agency said.
One woman in the town said the attackers had burned down her home but said they did not want to kill women.
"They said they were attacking because Muslims' lands were being taken," she told AFP.
Suspect freed
The Red Cross said another nine people - eight civilians and one police officer - were killed in Gamba, and one person was also missing. The ministry said 20 had died there.
Gunmen broke into the town's police station, reportedly freeing at least one suspect who had been detained over a deadly al-Shabab-claimed attack two weeks ago.
One police source told Reuters it was not yet clear how many detainees had been released.
Attacks in the Lamu area early last month killed at least 60 people, as gunmen descended on hotels and a police station near Mpeketoni, and attacked locals as they were watching a World Cup match.
Timeline of Somali raids in KenyaAl-Shabab has said it carried out the attacks in retaliation for Kenya's military actions against its operations in Somalia.
September 2011: UK national Judith Tebbutt kidnapped and her husband David killed in raid on Kiwayu island, north of Lamu. She was released six months later by a pirate gang
October 2011: Kenya sends troops into Somalia following Tebbutt's kidnapping and cross-border raids by al-Shabab; Al-Shabab warns of revenge attacks
Since then, numerous attacks in Nairobi, Mombasa and north-eastern region of Kenya, inhabited by ethnic Somalis
September 2013: At least 67 people killed after al-Shabab militants take control of Westgate shopping centre in Nairobi
May 2014: UK issues travel advisory, warning of increased risk of terror attack in Nairobi and coastal areas - UK tourists evacuated
June 2014: At least 48 people killed in raid on Mpeketoni
But Kenya's President Uhuru Kenyatta has blamed the Mpeketoni attacks on political networks. Opposition parties have dismissed the president's claims.
Comment: Mr. Uhuru is of course on to something which his western friendly opposition downplay in order for the message of 'be afraid now we don't have a government with western terror fighting allies at our disposal', to run its course.
The local al-Qaida fraction of al-Shabaab is of course linked to western intelligence:
The MI6 - Al-Shabaab Connection
Kenya al-Shabaab attack 'was led by white man speaking fluent British English'
Nairobi Westgate Mall massacre 'mastermind' was given cash, weapons and training by CIA and MI6 - Also served as regional recruiter for 'War on Terror' fodder