Authorities in Kenya say four people were killed on Thursday night by al-Shabab militants in a quarry in the northern border town of Mandera, news agency AFP reports.
The assailants shot and hacked the victims who are said to be non-Muslims.
The regional police boss Mohamud Saleh said an operation had been launched to pursue the attackers.
“We suspect al-Shabab and we are pursuing them,” he is quoted as saying.
A police source told AFP that 10 assailants took part in the attack, adding they “opened fire indiscriminately at the workers” in the quarry.
The source said several others were injured.
The national police boss Charles Owino said security services had information about an impending attack and had beefed up security but “no-one knew exactly where”.
The report says that the militants are now believed to have crossed the border into neighbouring Somalia.
Al-Shabab militants have attacked the Mandera several times, a situation that is forcing residents – mostly-non Muslims – to flee the area.