International experts have announced that Chilean Nobel laureate Pablo Neruda did not die of cancer, but could not conclusively determine if he was assassinated by late dictator Augusto Pinochet's regime.

Neruda, a celebrated poet, politician, diplomat and bohemian, died in 1973 aged 69, just days after Pinochet, then the head of the Chilean army, overthrew Socialist president Salvador Allende in a bloody coup.

The writer, who was also a prominent member of the Chilean Communist party, had been preparing to flee into exile in Mexico to lead the resistance against Pinochet's regime.

He died in a Santiago clinic where he was being treated for prostate cancer.

"The (death) certificate does not reflect the real cause of death," Aurelio Luna said at a news conference on behalf of a panel of experts, referring to the official explanation that cancer killed the famed writer.

Doubts emerged in 2011, when his former driver and personal assistant claimed Neruda was given a mysterious injection in his chest just before he died.

Pinochet, who ruled Chile for 17 years, installed a regime that killed some 3,200 leftist activists and other suspected opponents.

He died in 2006 aged 91 without ever being convicted for the crimes committed by his regime.

The group of 16 experts from Canada, Denmark, the US, Spain and Chile, 12 of whom worked in Santiago while the rest worked from abroad, could neither confirm nor rule out the hypothesis that Neruda was murdered.

"We do not have that definitive conclusion, we do not have the determination that there was indeed intervention of third parties," said investigating Judge Mario Carroza, who is handling the case.

The experts discovered bacteria that is already being studied in labs in Canada and Denmark, and could offer more insight into the cause of Neruda's death.

"We are waiting to precisely establish the origin and whether it is bacteria that comes from a laboratory, modified and cultivated for the purpose of use as a biological weapon," Mr Luna said.

Following the exhumation of Neruda's remains in 2013, studies in Chile and abroad discovered Staphylococcus aureus, a highly-infections bacteria that can be lethal, but not conclusive evidence that it was the cause of death.

The investigation began in 2011 after Manuel Araya, Neruda's former driver and personal assistant, claimed that he was given a mysterious injection in his chest just before he died.

"Neruda was assassinated," Mr Araya told AFP in 2013.

His assertion is supported by the Neruda family, which maintains a lawsuit seeking to clarify the circumstances of Neruda's death.

Neruda won the Nobel prize in 1971 "for a poetry that with the action of an elemental force brings alive a continent's destiny and dreams," in the words of the award committee.

He is remembered especially for his sensual, longing love poems.