(CNN) At least 273 people have died and 2,000 have been injured in the unrest that's rocked Nicaragua since April, according to the human rights arm of the Organization of American States (OAS).

The death toll includes two men killed Friday night in Managua in an hours-long attack by pro-government forces on protesters at the National Autonomous University of Nicaragua, the strongest protest holdout in the capital, said Paulo Abrao, executive secretary for the Inter-American Commission on Human Rights (IACHR), part of the OAS.

The protesters, who the government labeled as terrorists, had sought refuge inside a Catholic church and at least one of them died inside the parish as the church was hemmed in by gunfire, Abrao said.

The standoff at Divine Mercy Church was the latest in a series of violent clashes that started in April when the Nicaraguan government announced changes to the social security system regarding pensions.

President Daniel Ortega, who is been in power for 11 years, backed down a few days later, but the government's heavy-handed repression of the protests and the rising death toll ignited a national movement demanding Ortega's resignation.

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