Photos of Bieber-Gomez kiss spur threats

Although Disney starlet Selena Gomez, 18, has downplayed her relationship with teen heartthrob Justin Bieber, 16, calling him "one of my best friends" and not a romantic partner, the couple caused a commotion Monday after pictures surfaced of the two kissing in their bathing suits aboard a private yacht off St. Lucia. They were photographed Thursday while vacationing in the Caribbean.

The photos, which include other clothed public displays of affection, resulted in a burst of Twitter-verse vitriol from, presumably, Bieber's teen and tween fans - some of whom posted what appear to be hyperbolic but still troubling death threats.

While Gomez's own Twitter account contains no negative posts, TMZ.com collected a series of violent tweets, including three that read:

* roses are red, violets are blue, @selenagomez if you'll break @justinbieber's heart I'm gonna kill you

* @selenagomez I'll kill you I swear on GOD!!!!

* @selenagomez If you are the Girlfriend of Justin I will Kill you I HATE YOU :@ !!!

Gomez's representatives did not return calls for comment.

SEE PHOTOSJustin Bieber through the years

Pop singer Bieber and Disney Channel "Wizards of Waverly Place" star Gomez have been spotted arm in arm together often in the past few months, sparking couplehood speculation. Gomez consistently has insisted the two are just friends, telling celebrity-gossip blogger Perez Hilton jokingly in September, "He's, like, 16; I'm 18. That's illegal now!"

Nearly a year ago, when the two were 17 and 15, she told MTV News, "I feel like a big sister now, 'cause I want to protect him."

Bieber told People magazine last month, "We just like to hang out. [People] shouldn't be stopping us from going out to dinner and things like that."