A woman was tortured and beheaded by an angry mob in Papua New Guinea for allegedly practising witchcraft.

Helen Rumbali and three female relatives were taken from their home by villagers armed with machetes, guns and axes.

They burned down the house and took the women away to be tortured for allegedly killing another villager with black magic.

Rumbali, who is believed to have been in her 40s, her two teenage nieces and her older sister were slashed with knives. The three women were released after negotiations with police but Rumbali, a teacher, was beheaded publicly.

The mob said they had proof she was a witch because the grave of a villager who died had marks suggesting that black magic had been used. A swarm of fireflies led them to Rumbali's home, a sign of sorcery, according to local beliefs.

Witch-hunts in Papua New Guinea are common and appear to be spreading. In April, two women were tortured and beheaded for witchcraft - they had allegedly practised sorcery that resulted in the death of a former teacher.

In February, a mob stripped, tortured and tied up a woman accused of witchcraft and then burned her alive in Mount Hagan, the country's third-largest city.

Government officials said they did not understand why violence was increasing towards those accused of witchcraft but some have argued that a mining boom has increased economic tensions.

Jealousy causing hatred

Helen Hakena, chair of the North Bougainville Human Rights Committee, said: "Jealousy is causing a lot of hatred. People who are jealous of those who are doing well in life resort to what our people believe in - sorcery - to kill them."

Hakena said witchcraft was used as an excuse to kill Rumbali as her family were well off. Villagers had become jealous because Rumbali's husband and son had good jobs with the government, the family was educated and their home was of superior construction to other village houses.

Until May, the 42-year-old Sorcery Act allowed a belief in black magic to be used as a defence in court. The law was abolished in the face of growing violence towards so-called witches.

Police inspector Cletus Tsien said: "We know that this family was wealthy. We know that maybe there were bits and pieces of jealousy. We know they were accused of sorcery but there's no concrete evidence as to which factor contributed to the death."