Singer Justin Bieber attends the premiere of his girlfriend, Selena...

Singer Justin Bieber attends the premiere of his girlfriend, Selena Gomez's new movie, "Monte Carlo," screening at the AMC Loews Lincoln Square in Manhattan. (June 23, 2011) Credit: Getty Images

Justin Bieber's representative Wednesday unequivocally denied a fan's claim that the teenage singer is the father of her nearly 4-month-old son.

"It's sad that someone would fabricate malicious, defamatory and demonstrably false claims," Bieber's spokeswoman, Melissa Victor, said in a statement. "We will vigorously pursue all available legal remedies to defend and protect Justin against these allegations."

Bieber himself tweeted that he is "going to ignore the rumors" and focus on the release of a new Christmas album for which "[I'm] giving [a] portion of the proceeds to charity."

Mariah Yeater, 20, filed a paternity lawsuit against Bieber Monday in San Diego, claiming that a backstage tryst after Bieber's Oct. 25, 2010, concert at the Staples Center in Los Angeles led to the birth July 6 of Tristyn Anthony Markhouse Yeater.

Star magazine first reported the allegations, and sister company RadarOn line.com Wednesday posted the court documents.

Also Wednesday, E! Online posted the San Diego County birth certificate naming Mariah Laci Yeater as the mother but with the father's name left blank.

Yeater is asking the court to order Bieber to "undergo a paternity test to scientifically confirm that he is in fact the father of my baby" and to "provide adequate support for my baby."

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