The founder of the controversial Unification Church is in a South Korean hospital in critical condition due to complications from pneumonia, his spokesman said on Thursday.
Sun Myung Moon, 92, was admitted to Seoul's St Mary's Hospital on Tuesday and has been unconscious since then, Ahn Ho-Yeol told AFP, describing his condition as very critical.
"He is on life support and cannot communicate... doctors say the next three days will be the critical period," Ahn said. Close family members, including Moon's son and successor as church leader Hyung Jin Moon, were at his bedside.
The church's website posted a message urging the faithful to hold special prayers from Thursday until September 24 for the recovery of "the true father", including a three-day fast beginning Friday.
The Unification Church -- founded in Seoul in 1954 and officially called the Family Federation for World Peace and Unification -- is one of the world's most controversial religious organisations.
Its devotees are often dubbed "Moonies" after the founder and it is widely known for conducting mass weddings among followers involving thousands of couples.
It says it evangelises in some 200 countries and according to another spokesman has some three million followers worldwide.
The church's vast business empire includes The Washington Times newspaper and the New Yorker Hotel in Manhattan.
Hyung Jin Moon, the youngest of Moon's seven sons, succeeded his father as the church's most senior leader in 2008 at the age of 28.
Sun Myung Moon, who was born in North Korea, visited the North in 1991 to meet its then-president Kim Il-Sung.