Justin Bieber has admitted that he has "always felt unworthy" following recent concerns for his health.

The 31-year-old has sparked worry from fans over the last few months due to his seemingly-gaunt appearance and a string of bizarre posts on social media, including a video where he rapped shirtless about getting high.

The singer, who shot to fame at just 13 years old, issued a message on Instagram which offered an insight into judgmental thoughts he has about himself.

He wrote: "People told me my whole life 'wow Justin u deserve that' and I personally have always felt unworthy like I was a fraud, like when people told me I deserve something.

"It made me feel sneaky like damn if they only knew my thoughts - how judgmental I am, how selfish I really am, they wouldn't be saying this.

"I say all this to say. If you feel sneaky welcome to the club. I definitely feel unequipped and unqualified most days."

Last month a representative for Bieber categorically denied that the star uses hard drugs and described speculation about his appearance as "exhausting and pitiful and shows that despite the obvious truth, people are committed to keeping negative, salacious, harmful narratives alive".