Rihanna is firing back after a British tabloid claimed a sexy Armani ad purportedly showing RiRi's butt and boobs is not of the singer's but that of a body double -- Irish model Jahnassa Aicken.

The Sun claimed Jahnassa, 27, signed an agreement precluding her from talking about the Armani ad.

Jahnassa's torso, body and bum appear in parts of the ad, a source close to the Irish model told The Sun. It's shocking Rihanna wanted one considering she loves posing with no clothes, plus she's in great shape.

The 24-year-old Barbadian-born Rihanna insists the claims are false and took to Twitter to slam the Sun's story -- and took a few digs at Jahnassa in the process.

Ok @thesunnewspaper, this is the only way I could say this to you!!! F--- YOU....AND yo baggy -ss condom, Rihanna tweeted to her more than 20 million followers.

Who is Jahnassa. Does she have a tat on her hand too, RiRi continued an hour after the tweet about the Sun's story, referring to Rihanna's distinguishing tattoo on her hand.

The Sun is making the claims in part due to the photos from the shoot, which the tabloid says shows a woman with a fuller figure in a portion of the ad where the woman's head is not visible. Another shot, with Rihanna's face in clear view, shows a woman with a smaller frame, the Sun claims.

The tabloid claimed the Armani ad isn't the first time Jahnassa served as Rihanna's body double.

The Sun said Rihanna's people used the Irish model as a stand-in for Rihanna's We Found Love video in Northern Ireland after they spotted her in a crowd.

When told by Twitter user @BeckiFenty that Jahnassa was trending worldwide on the micro-blogging site, Rihanna tweeted, I pitch with a grenaade!

She then put an end to her Twitter tirade.

OK enough of that! I coulda been more clever about it, but I was lazy, RiRi tweeted.

Decide for yourself which side you think is telling the truth by viewing photos from the sexy Armani ad here.

The Rihanna body double controversy may be probed, the Sun reported.

If we have complaints consumers have been misled by the use of a body double, we will investigate, a spokesman for the UK's Advertising Standards Authority told the tabloid.