11/02/2011 at 10:00 AM EDT
Before he started dating girlfriend Selena Gomez
, a 20-year-old female fan says Justin Bieber
lost his virginity to her backstage and is the father of her 3-month-old child, according to new reports.
But the "Baby" singer, 17, dismissed the paternity allegations as "rumors" and "gossip."
"I'm gonna focus on the positives ... the music," he Tweeted
Wednesday in reference to his Christmas album, Under the Mistletoe
, released Tuesday.
The allegations are further complicated by the age gap between Bieber and Mariah Yeater, the fan making the claims. In California, the age of consent is 18, and the teen idol would have been 16 when the alleged sexual encounter occurred.
According to reports, Yeater says she was whisked away by a security guard to meet Bieber following an L.A. tour stop. "Immediately, it was obvious that we were mutually attracted to one another, and we began to kiss," the paternity suit alleges, according to papers obtained by a tabloid. "Shortly thereafter, Justin Bieber suggested that I go with him to a private place where we could be alone."
Yeater alleges Bieber told her he didn't want to use protection because it was his first time having sex.
She is seeking financial support from Bieber.
A rep for the pop star tells PEOPLE that his camp hasn't reviewed the lawsuit yet. "It's sad that someone would fabricate malicious, defamatory and demonstrably false claims," the rep says in a statement. "We will vigorously pursue all available legal remedies to defend and protect Justin against these allegations."
Meanwhile, a Bieber source says the woman's story just doesn't add up. "The kid is never alone. There's always someone with him," the source says. "He's never met this woman."