MANDERA, Kenya, July 7 -- At least 14 people were killed and 12 others injured early Tuesday in a suspected Al-Shabaab terror attack in Mandera county close to the Somali border.

Mandera County Commissioner Alex Ole Nkoyo confirmed the early morning attack, saying that unknown gunmen hurled grenades into a residential building located about 2 km from Mandera Town.

"Thirteen males and one female, mostly construction workers, were killed in the dawn attack. Twelve have been evacuated and rushed to a hospital," Nkoyo told Xinhua over telephone.

"We still don't know those behind the attack, but we have launched a manhunt for the killers who escaped immediately after the incident," he said.

"The deceased were caught unaware. They (Attackers) shot in the air several times and even used petrol bombs to carry out the attack. Most people were sleeping in tents outside their houses because the weather condition in Mandera is very hot," NKoyo added.

Sources said suspected Al-Shabaab militants first hurled several improvised explosive devices (IEDs) before opening fire on the quarry workers who were sleeping at that time.

The government late last year ordered quarry workers to leave the quarries and move to town for security reasons after 36 of them were killed in December.