People reported the couple were spotted at New York boutique Jacob & Co on Friday, and the heiress left with a $25,000 diamond-encrusted band.
A source told the website: 'They shopped for engagement rings. They were really cute together. Paris was making comments about the rings and joking that her ring has to be at least 24 carats.'
However, a spokesperson for Hilton insisted the ring was simply a birthday present: 'The couple were shopping in New York looking for something special for Paris's 30th birthday.'