Three-day mourning period as Afghanistan vice-president dies
Government spokesman Aimal Faizi confirmed the death of Mr Fahim, an ethnic Tajik who was part of the alliance that ousted the Taliban in 2011 and also served in President Hamid Karzai's first administration, in a tweet.
Mr Faizi said the government has called for a three-day mourning period.
Presidential candidate Hedayat Amin Arsala said the death "will affect the future political development" but he did not elaborate.
Mr Fahim was best known as an ally of Ahmad Shah Massoud, the charismatic Northern Alliance commander who was killed in an al Qaida suicide bombing two days before the September 11 2001 attacks.