Justin Bieber has apologised to fans after cancelling a string of planned appearances.

Justin said: "My apologies to @colbertlateshow as I won't be able to make it to nyc tomorrow for the show. I look forward to making it up to you soon. (sic)"

Later, he thanked his fans for their understanding, though he again declined the chance to explain the problem.

He wrote: "@StephenAtHome thank you for the understanding as sometimes life kicks our ass and we need to deal with it. I will see u soon. Thank you (sic)"

Gossip website TMZ said Justin has been on an emotional roller-coaster in recent weeks and simply could not continue with his hectic schedule.

The announcement comes shortly after it was reported Justin serenaded his ex-girlfriend Selena Gomez in a hotel bar.

The on/off couple were seen at the Montage Hotel in Beverly Hills, where Justin sang a number of songs, including 'My Girl' and his own tune 'Sorry'.

And Justin recently admitted he will always love the singer.

He said: "[She] is someone I love dearly. I'm never going to stop loving her. I'm never going to stop checking in on her.

"I don't think if you end a relationship, you should end that, unless it was super toxic and you guys were hurting each other physically or mentally. We always respected each other and we still respect each other."