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.