John McCain's running mate Sarah Palin said Monday that her 17-year-old unmarried daughter is five months pregnant, an announcement campaign aides said was aimed at rebutting Internet rumors that Palin's youngest son, born in April, was actually her daughter's.That would make Sarah Palin a grandma.

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

The father was identified in the statement as Levi, but the campaign said it was not disclosing his full name or age or how he and Bristol know each other, citing privacy.

Sarah Palin's fifth child, a son named 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 44-year-old Alaska governor, claimed to be the mother.

Palin spokesman Bill McAllister emphatically denied those rumors, and McCain adviser Mark Salter said the campaign announced the daughter's pregnancy to rebut them.