Peruvian police on Monday fired tear gas and clashed with protesters marching against the pardon of ailing ex-president Alberto Fujimori, who was serving a 25-year sentence for human rights abuses.

Current President Pedro Pablo Kuczynski ordered the pardon of Fujimori and seven other prisoners on Sunday on humanitarian grounds, once again placing himself in the middle of a political crisis just days after he avoided impeachment.

On Monday, protesters called for the departure from office of Kuczynski, who later defended his decision in a televised message to the nation.

"Out, out PPK! Out, out PPK!" angry demonstrators chanted in reference to the president, who had promised during his electoral campaign the previous year that he would not free Fujimori.

"Fujimori, murderer and thief. No to the pardon!" read one of the signs held by the protesters, some of whom also carried a giant Peruvian flag.

Relatives of victims of Fujimori's brutal rule took part in the march.

"We are here as relatives to reject this illegal pardon, because it does not correspond to the gravity of the crimes," Gisella Ortiz, representative of a group of families of victims, told reporters.

A strong force of anti-riot police moved through the streets of Lima and sought to prevent the demonstrators from heading to the clinic where Fujimori is hospitalized, firing tear gas canisters and erecting barricades to disperse them.

A cameraman from the state television station TV Peru was beaten by police and was being treated in hospital, the station's president Hugo Coya wrote on Twitter.

- Failed impeachment bid -

On Monday night, Kuczynski defended his decision to pardon Fujimori.

"I am convinced that those of us who feel democratic should not allow Alberto Fujimori to die in prison, because justice is not revenge," Kuczynski said.

"It is about the health and chances of life of a former president of Peru who, having committed excesses and grave errors, was sentenced and has already completed 12 years" in prison, he said.

The president had earlier said his decision to grant the pardon relied on a medical evaluation that Fujimori suffered a progressive and incurable illness and that conditions in prison "represent a grave risk to his life."

But the move came after Fujimori's son Kenji drained votes away from a parliamentary bid Thursday to impeach Kuczynski on suspicion of corruption, sparking speculation the pardon was political.

The condition of Alberto Fujimori, 79, was "delicate" and "a decision will be made" based on how he responds to treatment at the Centenario Clinic, a doctor at the facility, Alejandro Aguinaga, told reporters.

He said there was no prospect of Fujimori leaving soon.

Fujimori was transferred from his cell to a clinic Saturday suffering from low blood pressure and an irregular heartbeat.

"He remains in intensive care. His condition is favorable but other tests are necessary," Aguinaga said.

He said the ex-president had already undergone scans of his brain and heart, and stated that the cardiac problem was accentuating "various degenerative pathologies."

- Brutal, undemocratic reign -

Fujimori has been hospitalized on several previous occasions, the last time in September, and has had heart, back and stomach trouble as well as several operations to remove cancerous growths from his tongue.

The former leader has spent more than a decade imprisoned for ruthlessly cracking down on political rivals and for ordering dozens of murders and overseeing other brutal tactics.

Despite his conviction for human rights abuses, however, Fujimori retains a level of popularity in Peru for having defeated left-wing guerrillas and for stabilizing the economy after a period of crisis.

That dichotomy has come to the fore with the pardon: dozens of supporters gathered in front of the hospital looking after him, while opponents later demonstrated in Lima against him.

Fujimori, of Japanese descent, ruled Peru between 1990 and 2000. His reign quickly became autocratic after a 1992 internal coup in which he dissolved the legislature.

The pardon was Kuczynski's first major act after surviving the impeachment bid that was spearheaded by Kenji Fujimori's sister, Keiko, who is also a legislator and who narrowly lost the last presidential election.

Kuczynski, a former Wall Street Banker, was accused of lying to cover up $5 million in payments received from disgraced Brazilian construction firm Odebrecht.

He faces a struggle to influence Peru's opposition-dominated Congress, where his party has just 18 seats.