Ted Kennedy goes in for brain surgery in cancer fight, but vows he will return to help Obama win the White House

The 76-year-old Massachusetts senator said in a statement he would have "targeted" surgery at Duke University Medical Center in Durham, North Carolina, followed by chemotherapy and radiation at Massachusetts General Hospital in Boston.

Surgery was to start this morning and was expected to last about six hours, media reports said.

Kennedy, the youngest brother of assassinated U.S. President John F. Kennedy, said he expected to be hospitalized at Duke for about a week.

Fighter: Edward Kennedy gives a thumbs up as he walks out of Massachusetts General Hospital with his daughter Kara (far left), his son Patrick Kennedy (centre) and his wife Victoria

He was diagnosed with a malignant brain tumor called a glioma, a type of tumor that usually kills within three years, after suffering a seizure on May 17 at his family  compound at Hyannisport in his home state of Massachusetts.

Kennedy, who has been a senator for 46 years, is one of the most respected figures in U.S. politics and news of his condition prompted a wave of shock and sympathy in Washington.

"I am deeply grateful to the people of Massachusetts and to my friends, colleagues and so many others across the country and around the world who have expressed their support and good wishes as I tackle this new and unexpected health challenge," Kennedy said.

He added that the surgery would be performed by Dr. Allan Friedman, chief of neurosurgery at Duke.

"After completing treatment, I look forward to returning to the United States Senate and to doing everything I can to help elect Barack Obama as our next president," said Kennedy, who until the diagnosis had actively campaigned for Obama in his bid to win the Democratic nomination.

Kennedy has been a vocal critic of Republican President George W. Bush, particularly on his Iraq war, tax cuts for the wealthy and conservative nominees to the U.S. Supreme Court who he fears will push the high court to the right.

Kennedy came to the Senate in November 1962 to fill a seat earlier held by his older brother, then-President John Kennedy.

Support: Barack Obama waves beside Senator Edward Kennedy during a rally in Washington. Mr Kennedy has vowed to help get Mr Obama elected president