Ashton Kutcher with wife Demi Moore (WENN.COM)

Ashton Kutcher has taken aim at a U.S. tabloid over reports he's cheating on his wife Demi Moore.

In a new article, Star magazine suggests the actor's five-year marriage is "in danger of falling apart" following the "bombshell news" that the actor was "caught cheating with a sexy, young 20-something".

An eyewitness tells the publication he saw Kutcher "kissing and groping a hot young blonde" at Italian restaurant Madeo in Los Angeles.

The source says, "He was totally making out with her. I was shocked to see him sucking face with a girl who obviously wasn't Demi."

Kutcher himself has taken to Twitter.com to address the scandal, writing, "STAR magazine - you don't get to stand behind 'freedom of the press' when you are writing fiction."