ST. PAUL, Minn. — John McCain's running mate Sarah Palin said Monday that her 17-year-old unmarried daughter is five months pregnant, an announcement aimed at rebutting Internet rumors that Palin's youngest son, born in April, was actually her daughter's.

A statement released by the campaign said that Bristol Palin will keep her baby and marry the child's father. Bristol Palin is five months pregnant, and the baby is due in late December.

"Our beautiful daughter Bristol came to us with news that as parents we knew would make her grow up faster than we had ever planned. We're proud of Bristol's decision to have her baby and even prouder to become grandparents," Sarah and Todd Palin said in the brief statement.

"Bristol and the young man she will marry are going to realize very quickly the difficulties of raising a child, which is why they will have the love and support of our entire family," they added.

Sarah Palin's son Trig was born in April with Down syndrome. Internet bloggers have been suggesting that the child was actually born to Bristol Palin but that her mother, the Alaska governor, claimed to be the mother.

McCain adviser Mark Salter said the campaign announced the daughter's pregnancy to rebut those rumors.

Senior McCain advisers said the Arizona senator and his top aides had known about Bristol's pregnancy before offering Palin the No. 2 spot on the GOP ticket.

"Senator McCain's view is this is a private family matter. As parents, (the Palins) love their daughter unconditionally and are going to support their daughter," said McCain spokesman Steve Schmidt.

Said Schmidt: "Life happens."