MANAGUA (Reuters) - Nicaragua’s government said it released 636 prisoners on Tuesday as embattled President Daniel Ortega seeks to consolidate his hold on power nearly one year since the beginning of the biggest protests to shake his government.

A demonstrator holds a national flag during a march to mark the one year anniversary of the protests against Nicaraguan President Daniel Ortega's government, in Managua, Nicaragua April 17, 2019.REUTERS/Oswaldo Rivas

The gesture came on the eve of a march organized by Ortega’s political opponents that the government has deemed illegal, potentially marking a new flashpoint in the conflict.

The protests first erupted last April when Ortega, a former Marxist guerrilla, tried to cut welfare benefits. The protests soon spiraled into a broader resistance movement and became the sharpest test of his authority since he took office again in 2007.

The prisoners were freed from various prisons in Nicaragua and will finish their sentences under home arrest, the government said in a statement. The terms of the release mean they cannot attend protests or other public gatherings.

The government said the group includes 36 who were arrested during previous protests, but that none were political prisoners. The Civic Alliance, an opposition group, said in a statement, however, that 18 such detainees were released.

All the political prisoners released came from the prison in Managua known as La Modelo, according to Brenda Gutierrez, a member of the Comite Pro Liberacion de Presos Politicos, a group working for the release of political detainees.

State-controlled news network El 19 Digital said around 200 prisoners in total were released from La Modelo. A government spokesman did not reply to a request for details on where the other prisoners were released.

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The opposition wants the government to honor a pledge to release hundreds of prisoners still in custody who were detained during the protests of the past year.

At least 324 people have been killed in the disturbances, according to the Inter-American Commission on Human Rights, an autonomous arm of the Organization of American States.

Ortega has called the protests an illegal plot by his adversaries to oust him, while critics have accused him of increasingly authoritarian tendencies.

The government prohibited the opposition march planned for Wednesday afternoon on the grounds that those behind it were involved in “grave disturbances to public order” in past protests.

But organizers appeared determined to ignore the state-ordered prohibition.

“Today more than ever we call on the people to mobilize and express their desire for freedom in the most civic and peaceful way,” the opposition National Unity coalition said in a statement on Tuesday.

The march scheduled for Wednesday, as well as other opposition events set for Thursday and Friday, could reignite civil unrest. Thursday will mark a year since the start of the protests.

The anniversary coincides with Christian commemoration of Holy Week, and the gatherings associated with it have often provided venues for public demonstrations.

U.N. human rights chief Michelle Bachelet, a former president of Chile, has warned that the marches this week could turn violent. In a statement on Tuesday, her office noted that some 62,000 Nicaraguans had been displaced over the past year and that hundreds more had been arrested.

A Cold War adversary of the United States, the 73-year-old Ortega also served a single term as president in the 1980s.