Jennifer Aniston reportedly turned down Justin Theroux's marriage proposal.

The Hollywood stars have been dating for around 15 months and there has been intense speculation they will wed before the end of the year. According to the American edition of OK! magazine, Justin asked Jennifer to marry him during their recent romantic trip to Europe.

"She feels like she only got the proposal because she pushed for it. She doesn't want a guy marrying her because he feels some sort of pressure," a source revealed.

Jennifer apparently expected to receive an engagement ring at the famous Le Jules Vern restaurant atop the Eiffel Tower in Paris on June 13. However, Justin failed to pop the question and this left the 43-year-old actress feeling frustrated for the next few days.

"When it didn't happen Jen got upset, so they started bickering. They fought about his commitment issues and she brought up a bunch of stuff. He got defensive and stormed out, it was a big mess. They made up a few hours later, but it still ruined the mood of everything," the source added.

After the pair resolved their argument, Justin is believed to have surprised Jennifer by getting down on one knee when they were in Rome. However, he didn't get the response he was hoping for.

"Justin totally shocked her and proposed. She told him she loves him and wants to marry him, but she couldn't say yes," the source explained. "She wants everything to feel right, not rushed. She told him she feels like he's not ready, but she is willing to wait for him."

The pair recently sparked wedding rumours after Jennifer was seen wearing what appeared to be an engagement ring, but the speculation was later dismissed.