The leader of the rebel Revolutionary Armed Forces of Colombia (Farc) has cancer and will die within six months, according to a noted local journalist.

Pedro Marin, alias Manuel Marulanda, has led the Farc for over 50 years.

Respected Colombian journalist Patricia Lara said the 73-year-old had terminal prostate cancer, citing "very reliable sources" close to the Farc.

The news has prompted speculation about who will succeed him, and how it will affect the 40-year civil conflict.

Ms Lara - former editor-in-chief of the weekly Cambio magazine - said the leader had been very sick for several months and sought hospital treatment in neighbouring Brazil at the end of last year.

"Prostate cancer is attacking him with such ferocity that the old guerrilla leader no longer wants treatment," she said in an article in the weekly Diners magazine.

Mr Marulanda - known as Sureshot within the Farc for his unswerving aim - was last seen in public in August 2001 when he attended the now-defunct peace talks.

Undisputed chief

He co-founded the Farc in 1964. With its origins in small Communist peasant groups, the Farc officially declared its intention to use armed struggle to seize national power.

Over that time Colombia's security forces claim to have killed Mr Marulanda a dozen times.

Yet the wily leader has always escaped, building up the Farc from a handful of friends and cousins to a 16,000-strong force that dominates almost 40% of the country.

While the Farc is ruled by a seven-man secretariat, Mr Marulanda has been the undisputed chief.

A struggle for power within the guerrillas has been going on for many years to decide who will succeed him, says the BBC's Jeremy McDermott in Colombia.

Possible successors include the Farc's field marshal, Luis Suarez, alias El Mono Jojoy, and Luis Edgar Devia, alias Raul Reyes, the group's senior negotiator and diplomat.

Our correspondent says that, no matter who wins the power struggle, there is little prospect that the guerrillas' 40-year war will end any time soon.