"This is unacceptable. People must not take the law into their own hands simply because they suspected someone," said Mwangi Ngunyi, the head of Nyamaiya district. "We will hunt the suspects down," he added.

The gang of about 100 people moved from house to house late Tuesday, tied up their victims and set them ablaze, the official said.

Ngunyi added that the mob also torched 50 houses in Nyakeo village, located some 300 kilometres (180 miles) northwest of the capital Nairobi.

"I can't believe my wife of many years would be killed so brutally by people who cannot prove their case even before God," said Enoch Obiero, a pastor.

"My mother has always been a role model to the entire village and why the mob had to kill her will remain a mystery to me forever," lamented 32-year-old Emily Monari.

The region, populated mainly by the Kisii tribe, has been dubbed Kenya's "sorcery belt" due to mob attacks on women suspected of witchcraft.

Efforts by the authorities to clamp down on vigilante and mob justice have been unsuccessful.

Dozens of suspected people were killed in western Kenya in the 1990s, amid allegations of sorcery.

Several cases were also reported in recent months in neighbouring Tanzania, forcing President Jakaya Kikwete to order special protection for albino, who were being murdered and mutilated for good luck by with-doctors.