US Democratic presidential nominee Barack Obama will halt his campaign for a day this week to visit his ailing 86-year-old grandmother in Hawaii, sources said.

Senior advisor Robert Gibbs announced the change in schedule during a campaign swing in Florida.

Obama's grandmother Madelyn Dunham's health has deteriorated and she is in a very serious condition, sources said.

Dunham had helped raise Obama.

Obama will be visiting her between Thursday and Friday and he will return to the campaign trail on Saturday.