, Oct. 27 -- Former US President Joe Biden on Sunday warned that the United States is going through "dark days" as he urged Americans to remain hopeful and defend democratic values.

Speaking publicly for the first time since finishing radiation therapy for aggressive prostate cancer, Biden said the country is witnessing attacks on free speech and the constitutional limits of presidential power under President Donald Trump.

He made the remarks while receiving the Lifetime Achievement Award from the Edward M. Kennedy Institute in Boston.

Biden said the United States has long stood as a "beacon" of an idea stronger than any army or dictator, but stressed that it depends on a presidency with limited authority, a functioning Congress and an...