Los Angeles: Shia LaBeouf's girlfriend Mia Goth has ignited rumours of an engagement with the actor after she was photographed flashing a diamond on her ring finger.

Shia LaBeouf
Shia LaBeouf. Pic/Santa Banta 

The "Nymphomaniac" actress was spotted at the LAX airport on Monday, reports aceshowbiz.com.

Both LaBeouf and Goth, who have been very private about their love life, have not yet addressed the engagement rumours.

The duo were co-stars in the 2013 two-part drama art film "Nymphomaniac" and have since been romantically linked. Neither of them is shy of showing off their love for each other as they were often caught on camera engaging in public display of affection.

They were last seen together having lunch in Studio City, California on Saturday.