'I know I failed': Justin Timberlake apologises to Britney Spears and Janet Jackson

Pop star Justin Timberlake has issued a public apology to his former girlfriend Britney Spears and singer Janet Jackson, saying he had failed them in the past.

Timberlake spoke out on his Instagram account after criticism this week on social and mainstream media of interviews he gave some 20 years ago about his relationship with Spears when both were at the height of their careers.

The backlash followed the broadcast of a TV documentary about the rise and fall of Spears, including how she was shamed in the media when their relationship ended in 2002.

Timberlake also has been dogged for years by accusations that he failed to take sufficient responsibility for the infamous "wardrobe malfunction" during the 2004 Super Bowl halftime show.

"I specifically want to apologise to Britney Spears and Janet Jackson both individually, because I care for and respect these women and I know I failed, " Timberlake wrote on Instagram.

The pop star, now married to actress Jessica Biel, said he was sorry for speaking out of turn, or not speaking up, for what was right in the past.

"I understand that I fell short in these moments and in many others and benefited from a system that condones misogyny and racism," he said.

Timberlake and Spears dated for about three years before splitting up abruptly in 2002.

In Friday's apology, Timberlake said the entertainment industry sets white men up for success.

"Because of my ignorance, I didn't recognise it for all that it was while it was happening in my own life," he said.

Spears' business and personal affairs have been controlled by court-appointed conservators since 2008.

Representatives for Jackson and Spears did not immediately respond to requests for comment on Friday.