An Afghan woman accused of adultery was executed by a purported member of the Taliban as a crowd of about 150 men looked on and cheered in a killing captured in video footage that surfaced at the weekend, Belfast Telegraph said.

The slaying occurred just an hour's drive from Kabul and is a grim reminder of the hardline group's brutality, under whose rule from 1996 to 2001 women suffered severe privations.

The video, obtained by Reuters, shows a woman wrapped in a shawl kneeling in the dirt. A turban-clad man approaches and fires on her at close range with an automatic rifle. Another man is heard saying: "Allah warns us not to get close to adultery because it's the wrong way. It is the order of Allah that she be executed."

The woman was involved – either by consent or force – with two Taliban commanders and was killed in order to settle a dispute between them, according Parwan's Provincial Governor Basir Salangi. According to Agence France Presse, the woman was a 22-year-old called Najiba. The fate of the Taliban commanders is not known.

"When I saw this video, I closed my eyes," Mr Salangi told Reuters. "The woman was not guilty; the Taliban are guilty." The footage is thought to have been shot about a week ago. Mr Salangi added that the Taliban have considerable influence in his province.

The footage emerged as international donors arrived in Tokyo yesterday and pledged $16bn (£10bn) in development aid over the next four years. The pledge of development aid is seen as an assurance that Western donors will not abandon Afghanistan after combat troops leave in 2014.

The UK is one of the top four donors – along with the US, Japan and Germany – and has said it will keep annual aid at £178m until 2017.

The aid money promised in Tokyo meets the financial requirement estimated by the World Bank. It is in addition to the $4.1bn in military assistance pledged by donors at a Nato conference in Chicago in May.

Multiple references to women's rights are included in the final Tokyo agreement, including a specific reference to monitoring the implementation of the Elimination of Violence Against Women Law and the National Action Plan for Women.