The South American country's justice department said in a statement that the Supreme Court had "issued the arrest and detention orders against former president Fujimori so that he may be re-integrated into the prison establishment."

He was pardoned last December on humanitarian grounds, but critics said the move was in exchange for Fujimori's son helping then-president Pedro Pablo Kuczynski avoid impeachment.

Fujimori was 12 years into a 25-year jail sentence handed down for ordering two massacres by death squads between 1991 and 1992.

"This decision is inhuman, it's unjust," said his daughter Keiko, leader of the main opposition Popular Force party and seen by many as the heir to Fujimori's political dynasty.

"Today is the saddest day of our lives, it's painful," a tearful Keiko told reporters, adding that she had yet to speak to her father since the court decision.

One of Fujimori's lawyers, Miguel Perez, said on Chile's RPP radio the decision was subject to appeal. 

The pardon, issued by Kuczynski before he was himself brought down by a corruption scandal, triggered a wave of protests by human rights organizations and by victims of Fujimori's crackdown. 

Fujimori, a Peruvian of Japanese descent, has been living in Lima but has been hospitalized four times since his release last December.

After his arrest Wednesday, he was admitted to a clinic for tests after experiencing a drop in blood pressure and an accelerated heart beat, his doctor, Alejandro Aguinaga, told reporters.  

- Health problems -

Victims of Fujimori's crackdown had petitioned the Inter-American Court to demand a judicial review of the process that led to the pardon.

Carlos Rivera, a lawyer for the victims, said the decision to annul the pardon was justified.

"Kuczynski's pardon to Alberto Fujimori has no legal value and therefore he has to return to prison for irregularities in the process," he said. 

Kuczynski had justified the pardon on humanitarian grounds, given Fujimori's well-documented ill-health. But the scandal-tainted president had only days earlier survived an impeachment vote thanks to the abstention of a group of lawmakers led by Fujimori's son Kenji. 

This lead critics to say the pardon was obviously a quid-pro-quo, the price Kuczynski paid for what proved to be a temporary political survival.

"International standards in the humanitarian pardon were not met," Rivera said.

Alejandro Aguinaga, Fujimori's doctor, expressed shock at the news. "We see that in Peru nothing is respected. The pardon of president Fujimori was a constitutional action," Aguinaga told Radio RPP.

Fujimori has had a number of operations as part of a long-running battle with tongue cancer. His most recent hospitalization was in August, for an irregular heartbeat.

- Family feud -

He has been working on a memoir about his decade in power (1990-2000), a period marked by corruption but also by a fight against guerrillas and terrorism.

"I have reached 80 bearing the marks of the years, with all the shocks of political life, the enormous satisfactions and the profound regrets," he wrote in a message to AFP around his birthday in July.

"In the few years I have left," Fujimori explained in his handwritten text, "I will dedicate myself to three objectives: bringing my family together, improving my health to the extent possible, and striking a serene and balanced equilibrium in my life."

However, Fujimori has been unable to reconcile his daughter Keiko, 43, with her younger brother Kenji, who leads a rival faction of her party, to end a political schism which could see the two face off in the 2021 presidential elections.

The charge of crimes against humanity stemmed in part from the killings or disappearances of scores of civilians -- allegedly by a shadowy squad of military officers -- during Peru's bloody struggle against Maoist rebels.

The ex-ruler is revered and despised in equal measure in Peru. Admirers laud him for dragging the country's economy into the modern era and defeating the Shining Path guerrilla movement.

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