Islamist militants from al-Shabab on Friday killed 12 people drilling a well in drought-ravaged southern Somalia, a local resident and official said.

The conflict between the al-Qaida-linked al-Shabab, which wants to implement a strict implementation of sharia, or Islamic law, and the central government has killed thousands of people since 2006.

Somali security forces say they have made gains on the battlefield in recent weeks while fighting alongside local self-defense groups, but al-Shabab has continued to conduct deadly raids.

The latest attack happened in the town of Gariley in the southern Gedo region when the militants attacked the crew at its work site, burning their bodies and drilling equipment, said Mahad Abdi, a local resident who visited the scene and counted the bodies.

The area is suffering from the Horn of Africa's worst drought in 40 years, leading the United Nations to warn of a looming famine.

"I am very sorry that al-Shabab is causing such trouble for us while we are suffering from drought and lack of water in our area and we don't want water 100 km away from us," Abdi told Reuters.

Mahmoud Abdel Warsame, the mayor of Gariley, confirmed the death toll and said security forces also killed six al-Shabab fighters.

Al-Shabab has in recent weeks burned houses, destroyed wells and beheaded civilians in other parts of central and southern Somalia, residents say.

The attacks, and the group's demands for tax payments despite the drought, have pushed some residents to take up arms against al-Shabab.

In a separate incident in the capital Mogadishu, al-Shabab fighters killed Mogadishu's head of police, his two bodyguards and a police-based journalist, President Hassan sheik Mohamud was reported as saying on Somali National News Agency.