Afghan police have arrested four people who allegedly tried to force a woman into prostitution in western Afghanistan and beheaded her when she refused, officials say.

Mah Gul, 20, was beheaded after her mother-in-law attempted to make her sleep with a man in her house in Herat province last week, provincial police chief Abdul Ghafar Sayedzada said.

Confessed... Najibullah. Credit:AFP

"We have arrested her mother-in-law, father-in-law, her husband and the man who killed her," he said.

Gul was married to her husband four months ago and her mother-in-law had tried to force her into prostitution several times in the past, Sayedzada said.