Calls mounted Monday for dozens of opposition figures jailed in Nicaragua to be freed after the death of a would-be presidential candidate fueled fears for the health and safety of others.

Hugo Torres, a 73-year-old former guerrilla companion of now-President Daniel Ortega, died in detention Saturday after concerns were repeatedly expressed for his well-being.

Other inmates, too, are in dire straits, according to family members and rights defenders who say the prisoners are malnourished, losing weight, teeth and memory, and getting weaker by the day.

"Many are facing a serious risk to health and life," former Inter-American Commission on Human Rights (IACHR) president Antonia Urrejola said on Twitter.

The European Union, via external affairs spokesman Peter Stano, called for "the immediate and unconditional release of all political prisoners... subjected to inhumane detention conditions" in Nicaragua.

And US State Department assistant secretary Brian Nichols said that "continuing to detain prisoners under these conditions, especially the elderly, is unacceptable. We urge their immediate release."

Costa Rican Foreign Minister Rodolfo Solano expressed "concern" about the health of the remaining detainees and in a statement urged Nicaragua to allow a visit by representatives of the UN High Commissioner for Human Rights.

The Organization of American States (OAS) said it "categorically condemns the persecution and arbitrary detention" of Nicaraguans and urged the immediate release of all political prisoners.

"The General Secretariat of the OAS considers the fact of keeping political prisoners, with terminal illnesses and without necessary medical assistance, an abominable act, violating their fundamental rights," it said in a statement.

Hugo Torres died eight months after his arrest with other opposition figures due to challenge President Daniel Ortega in national elections
Hugo Torres died eight months after his arrest with other opposition figures due to challenge President Daniel Ortega in national elections AFP / Oscar NAVARRETE

Torres, who had risked his own life to break Ortega out of jail in the 1970s during the struggle against the Somoza dictatorship, later became a critic of the president and entered opposition politics.

But ahead of elections last November in which Torres was to be a candidate, he was arrested along with dozens of other opposition figures -- seven of them presidential hopefuls.

The prosecutor's office did not state the cause of Torres's death, and said that he was transferred to a hospital "from the moment his health condition deteriorated."

But Monica Baltodano, a Torres ally now living in exile, said he was taken to hospital on December 17, already unconscious and long suffering ill health.

Jared Genser, a lawyer for some of the detainees, said from Miami that Torres's death was "completely avoidable and predictable" and "likely not the last."

In total, Ortega's government detained 46 opposition figures including Torres, accusing them of undermining Nicaragua's "national integrity."

To date, 18 have been found guilty and seven sentenced to prison terms of between eight and 13 years.

Another 124 detractors have been in jail since anti-government protests in 2018 met with a brutal crackdown that resulted in 355 deaths and more than 100,000 people fleeing into exile, according go the IACHR.

The Costa Rica-based rights advocacy group Center for Justice and International Law called for the "unconditional liberation" of Nicaragua's "political prisoners" and said Torres's death must not go unpunished.

Ortega, 76, was re-elected to a fourth consecutive term in November elections dismissed as an undemocratic "farce" by the international community, which tightened sanctions in response.