A United Nations human rights official says a three-member U.N. commission has arrived in Guinea to investigate the September massacre in which troops fatally shot pro-democracy demonstrators and raped women in broad daylight.

Sonia Muller-Rappard said the all-African commission arrived in Conakry on Wednesday. The group was appointed by U.N. Secretary-General Ban Ki-moon last month to determine who was responsible for the massacre.

A peaceful pro-democracy rally in the West African country on Sept. 28 took a violent turn when presidential guard troops opened fire on tens of thousands of demonstrators.

A Guinean human rights group said 157 people were killed. The government put the death toll at 57.