Pop singer and fashion designer Victoria Beckham told the United Nations that she was "very humbled" and "honoured" to act as a goodwill ambassador for the organisation's Aids campaign.

"This is the beginning of an incredible journey for me," she told reporters at the UN, in New York.

The former Spice Girl said she had been inspired talking to women in Cape Town.

"I came home and knew I had to do something," she said.

"It's taken me getting to 40 years old to realise that I have a responsibility as a woman, as a mother - I have a voice that people will listen to."