The former Disney star and Bieber were spotted over the weekend at Beacher's Madhouse in LA, where one eyewitness claimed the two flirted for several minutes before leaving together.
However, Cyrus cleared up the rumours, insisting that a romance between herself and long-time friend Bieber is "impossible".
"I'm engaged! I'm engaged. That is impossible," she said. The pop singer's comments also put an end to rumours that she and fiance Liam Hemsworth have split. Earlier this month, she was spotted once again wearing her engagement ring at a Los Angeles event.
J. Jayalalithaa passes away: Her life in pictures
Photos: Shah Rukh Khan, Deepika Padukone, Alia Bhatt at an awards show
Photos: Big B, Iulia Vantur at Himesh Reshammiya's album launch
Photos: Aamir Khan with 'Dangal' actresses at fashion show
Spotted: Twinkle Khanna, Shriya Saran at an event in Mumbai