Jamie Lynn Spears is pregnant again, it has been reported.[Agencies]

Britney Spears' sister Jamie Lynn - the 17-year-old star who gave birth to her first daughter Maddie Briann in June - is pregnant again, it has been claimed.

The actress was reportedly shocked to discover she is expecting her second child and has been trying to keep it a secret.

A source told National Enquirer magazine: "Jamie Lynn is about eight weeks pregnant, and she and her mum Lynne are hysterical. Neither of them knows what to do, but for now they're trying to keep the news from getting out.

"Jamie Lynn believed she couldn't get pregnant while she was breastfeeding. She'd expected to have her period by early September, but a home pregnancy test came back positive and Jamie Lynn cried her eyes out.

"Lynne was livid when she found out. She told Jamie Lynn that she thought she was smarter than that and she couldn't believe that she hadn't learned her lesson."

It has been claimed the Zoey 101 star's friends and family are urging her to terminate the pregnancy.

Meanwhile, Jamie Lynn has dismissed rumours her fiance Casey Aldridge got Kelli Dawson pregnant after they had an affair.

She told America's OK! magazine: "That is just completely fabricated. He never had an intimate relationship with her, so how would that be possible? Around here, that particular girl is known to make up stories. It hurt me to hear those things.

"My family know if I were in a relationship like that, I wouldn't put up with it. They support me, and they support Casey also."