A subdued Barack Obama on Monday mourned his grandmother as a "quiet hero" who helped raise him, telling a campaign rally that her death had made the final night of his White House campaign "bittersweet."

As the Democratic candidate arrived in North Carolina for his second-to-last rally before Tuesday's election, he announced that Madelyn Dunham, 86, had died peacefully at her home in Honolulu after a battle with cancer.

Obama's Republican rival, John McCain, issued a statement of condolence and also offered best wishes to Obama.

Obama has often referred to Dunham, who helped his single-mother take care of him, as the rock of his family and someone who shaped his values.

A little more than a week ago, he left the campaign trail for a 22-hour trip to Hawaii to say goodbye to her.

"This obviously is a little bit of a bittersweet time for me," Obama told an outdoor rally under drizzly rain as tears rolled down his cheeks and his voice choked up.

"She was somebody who was a very humble person and a very plain-spoken person," he said. "She was one of those quiet heroes that we have all across America. They're not famous. ... But each and every day they work hard."

Dunham helped raise Obama from the age of 10 while his mother was working in Indonesia.

Obama said after his Hawaii trip that he had been flooded with cards, flowers and well-wishes from around the country, and he regularly thanked crowds at his campaign rallies for their prayers.

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