(CNN) A march honoring Nicaraguans killed in violence surrounding recent anti-government demonstrations also ended in bloodshed Wednesday -- the country's Mother's Day.

"We've received grave claims of deaths and serious injuries that resulted from today's violence in Nicaragua," Inter-American Commission on Human Rights (IACHR) Executive Secretary Paulo Abrao tweeted Wednesday.

On Thursday, the Nicaraguan Center for Human Rights released a statement saying 16 people had been killed and 88 injured during the clashes. The march had been promoted as a peaceful demonstration by organizers.

Rights group Amnesty International, which had a delegation accompanying the march, said it "witnessed the chaos caused by the detonation of firearms," and accused police and pro-government groups, known as "Sandinista mobs," of carrying out attacks.

Civil unrest has plagued the Central American country since April, when massive protests broke out over proposed government reforms to the country's social security system.

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