The Sunday pardon came three days after abstentions by lawmakers from a party led by Fujimori's children caused the failure of a vote to impeach President Pedro Pablo Kuczynski. Fujimori, 79, was serving a 25-year sentence for the killings of 25 people in a campaign against the leftist Shining Path guerrilla group.

About 5,000 people protested across the country carrying posters with Fujimori's face and the words "murderer" and "thief."

Kuczynski was accused of lying about his financial ties to the Brazilian construction giant Odebrecht, which paid hundreds of millions in bribes to public officials across Latin America to win lucrative public works contracts. Fujimori's powerful lawmaker daughter, Keiko Fujimori, led the impeachment drive in Congress, but legislators loyal to the ex-president's son Kenji, also a lawmaker, killed the effort by abstaining.

Kenji Fujimori has long pushed for his father's release from prison and Kuczynski's opponents said the pardon was clearly payback for the abstentions that ended the impeachment drive. With Kuczynski under criminal investigation for his Odebrecht ties and weighed down by an 18% approval rating, observers said his long-term political survival still appears to be in jeopardy.

"The pardon opens a Pandora's Box; the haste with which it was taken makes Kuczynski even more vulnerable," said Jose Carlos Requena, an analyst with the political consulting firm 50+1.

Kuczynski's business, Westfield Capital, received $782,000 from Odebrecht more than a decade ago. Kuczynski had denied any ties to the company until the evidence was made public this year. He later said that none of the contracts in question contained his signature and that he had no knowledge of the payments.

Alberto Fujimori, president from 1990 to 2000, is remembered for stabilizing the economy and defeating the Shining Path, and for human rights violations and corruption.

He was moved to a clinic Saturday for what his doctors said was heart arrhythmia. His supporters said he would remain there until he was healthy enough to leave.