Mrs Obasanjo, 59, apparently had chosen to have an operation at the exclusive Molding cosmetic surgery clinic in the upmarket town of Puerto Banos near Marbella last Friday.
She was reported to have suffered a severe asthma attack and was rushed to hospital in Marbella in the early hours of Sunday morning, where she was declared brain-dead.
As the body of the wife of President Olusegun Obasanjo was being repatriated to Nigeria last night, however, the precise circumstances and cause of her death remained shrouded in mystery
The Molding, Marbella's biggest plastic surgery clinic, is the "health tourism" playground of many rich foreigners on the Costa del Sol. For many of them, it is the first choice for expensive plastic surgery treatments in luxurious surroundings.
Doctors at the clinic refused yesterday to say about the procedure undergone by Mrs Obansanjo. The clinic did, however, issue a statement, saying that she did not die during cosmetic treatment.
"At this moment we do not know the causes of Mrs Obansanjo's death and we await the results of the autopsy. We have given all information possible to those carrying out the autopsy," it said.
The daily newspaper El Pais reported that Mrs Obasanjo, looking for a way to lose weight, may have undergone liposuction, but when The Independent asked if this was the case, the clinic would not comment on the procedure she had undergone.
An initial post-mortem carried out over the weekend suggested Mrs Obansanjo might have died of a severe asthma attack. A more detailed, two-and-a-half hour-long, autopsy performed yesterday, gave a much clearer indication of the cause of death, said Antonio Garcia de Galvez, director of the Malaga Institute of Forensic Medicine, where the examination was carried out. The results will, however, remain secret and divulged only to the judge in charge of the investigation.
In Spain, autopsies are only court-ordered when the death is deemed to be of a suspicious nature - as in this case - or to have been caused by violence, Dr Garcia de Galvez said. Coroners investigating the cause of Mrs Obasanjo's death are looking for evidence of possibility of medical malpractice.
The official Nigerian media was yesterday filled with tributes for the woman who, over the past six years, came to occupy a formidable, if often controversial, role in public life through her work for children's charities and contribution to Nigeria's women's rights movement. There was little room yesterday for carping about her notorious extravagance and corruption- tainted lifestyle.
"The mother of the nation is gone," wrote Dr Ahmadu Ali, national chairman of the ruling People's Democratic Party (PDP) in a hastily arranged condolence register at the State House, Abuja.
Mrs Obasanjo, who would have turned 60 next month, became a familiar presence in Nigerian public life from the day her husband, who had taken several wives before her, took power in 1999. The couple had been separated in the early 1990s but were reunited during his imprisonment under the military dictatorship of Sani Abacha later in that decade.
Her wholesome reputation was, however, tainted earlier this year by allegations of corruption when she ordered the arrest of a newspaper publisher over an article entitled "Greedy Stella". Orobosa Omo-Ojo was detained after his newspaper, the Midwest Herald, ran an article accusing Mrs Obasanjo of organising the sale of 207 government-owned properties to her relatives at reduced prices.
During her lifetime Mrs Obasanjo also attracted widespread criticism for her ostentatious displays of wealth. That she should have apparently died after undergoing expensive cosmetic surgery in Marbella, the playground for Saudi princes and wealthy despots, will do nothing enhance her reputation.
Procedures that went wrong
* OLIVIA GOLDSMITH, Author of The First Wives Club, made into a hit film, died in New York in 2004 eight days after undergoing a face lift. She had a severe reaction to the anaesthetic.
* LESLIE ASH Former star of Men Behaving Badly, had collagen implants in her lips in 2003 which went wrong, giving her the nickname "trout pout". She described herself as having had "an accident".
* DENISE HENDRY Wife of the former Scotland football captain Colin Hendry, developed septicaemia after having a tummy tuck at a private hospital in Lancashire. She went into coma but recovered.
* HOPE DONAHUE Had 17 operations in five years and said she was addicted to the surgery in a memoir, Beautiful Stranger. Two operations went wrong, including implants that turned her chest into a hard block of scar tissue.
* JOCELYN WILDENSTEIN The divorcée, 56, was called the Bride of Wildenstein after she was said to have spent £2m on plastic surgery.