Mr. Fujimori, who is 79, suffers from arrhythmia and tongue cancer, among other medical problems, and was taken from prison to a hospital on Friday after his blood pressure dropped, doctors said.
The pardon is the latest development in Peru’s continuing political crisis.
Mr. Kuczynski granted the pardon just after he had narrowly escaped being impeached by Congress over accusations connecting him to a graft scandal in Latin America. The impeachment vote failed because a faction of Mr. Fujimori’s party led by his son Kenji abstained from the vote, denying Mr. Kuczynski’s opponents the supermajority required to remove him from office. The pardon was seen by some as a political reward to the son.
“I think that those of us who are committed to governance need an explanation,” said Congressman Richard Acuña, who abstained from the impeachment vote.
After the vote, Carlos Basombrío, the interior minister, announced his resignation. Now at least three lawmakers have come forward to say they will resign after the holiday because they oppose the president’s decision to pardon Mr. Fujimori.
“I do not agree with the decision,” Congressman Vicente Zeballos said. “It does not fit with my political convictions.”
As the democratically elected president of Peru in the 1990s, Mr. Fujimori led the country through a period of economic revival. But he was removed from office in a corruption scandal and later convicted of human-rights abuses that the military carried out in his name. If he serves his sentence to the end, he will be in prison for 14 more years, or until he is 93.
Even from prison, Mr. Fujimori has exerted influence on politics, and his supporters, so-called Fujimoristas, dominate the legislature. He also has supporters among Peru’s citizens.
On Sunday, people congregated on the street in Lima in front of the hospital where Mr. Fujimori is being treated. Dozens shouted their support for him as Mr. Fujimori’s daughter Keiko, who leads another faction in his party and is Mr. Kuczynski’s chief rival, arrived to visit her father, and stated her gratitude to Mr. Kuczynski.
But at the same time, anti-Fuijimoristas rallied near the Presidential Palace at Lima’s main San Martin Plaza holding signs that read “dictatorship, never again” and “illegal pardon equals impunity.”
Family members of victims in the human-rights case say they are upset about the pardon.
“It hurts, I’m angry,” said Gisella Ortiz, whose brother Luis Enrique Ortiz, who was dragged out of a dormitory at La Cantuta University, outside Lima, with eight others and killed by a death squad. “I didn’t think he’d barter impeachment for this pardon.”
Political analysts say the country is at a crossroad.
“The likely upshot is yet more severe cynicism — already at dangerously record levels — and more intense political polarization,” said Cynthia McClintock, a professor of political science at George Washington University.