The FBI has released most of its secret files on the late Senator Edward Kennedy.

Most of the documents relate to death threats made against Senator Kennedy, the Associated Press agency reports.

The files will be scrutinised for details about the senator's controversial car accident in Chappaquiddick, in which a female passenger was killed.

Senator Kennedy died in August 2009, aged 77, after battling brain cancer.

He was the last surviving brother of the storied political family.

President John F Kennedy was killed in Dallas, Texas, in November 1963, while Senator Robert F Kennedy was shot in a California hotel while campaigning for the presidency.

Most of the death threats against Senator Kennedy were made during his unsuccessful attempt to beat incumbent President Jimmy Carter for the Democratic nomination for President in 1980.

Ted Kennedy was the fourth-longest serving senator in US history, serving for 47 years.

A highly effectively lawmaker, his power and reputation earned him the nickname "the lion of the Senate".