Niall Horan has asked fans to "respect his privacy" while he recovers from a knee operation.

The One Direction singer took to his Twitter account to reassure his followers that he's doing well, but needs to keep well rested.

One Direction have their worldwide Where We Are tour coming up later this year and the Irish heartthrob says getting better for that is his main focus.

"Hey guys I know most of you have seen those pics today! Yes I've had major knee surgery , a much larger surgery than first anticipated

"But i would like to tell u , it was a complete success ! Considering the scale of it! So all I ask of you guys is that you would respect my Privacy as I try to recover and get for the where we are tour! (sic)" he posted to his 16.7million followers.

The 20-year-old underwent surgery in America, but flew back to the UK yesterday where he was spotted hobbling on crutches.

British newspaper The Sun has reported that Niall needed the surgery after repeatedly dislocating his knee as a child.

While fans flock to the social media site to wish Niall a speedy recovery, another member of One Direction has got into trouble for his online exploits.

Liam Payne was pictured balancing on the ledge of a 34-storey building in London in a photo on a friend's Twitter feed.

The sheepish 20-year-old then apologised to his fans, many of whom are young, for his "irresponsible" behaviour.

"You may have seen a photo of me today taken on top of a building. I regret being there and having a photo taken.

"It was a stupid and irresponsible thing to do. I am sorry, and do not endorse any fans trying to repeat this, as it is extremely dangerous (sic)" he tweeted.

"Worse things have happened, I'm sure we'll be fine ;)," he added cheekily.