Two university student protesters have been killed in Nicaragua in clashes over a social security reform pushed by President Daniel Ortega's government, according to independent media reports.
Police did not immediately confirm the deaths, but images of the two young men were carried in local media and repeated on social networks.
They came a day after a police officer, a protester and a pro-government activist became the first confirmed casualties of the violence.
Dozens more are believed to have been wounded or arrested based on video broadcasts, in days of unrest the like of which has become rare in the Central American nation and which elicited a heavy-handed response.
"The Nicaraguan state must fulfil its international obligations to ensure people can freely exercise their rights to freedom of expression and freedom of peaceful gathering and association," the UN's human rights office said in a statement.
The Organisation of American States issued its own statement of concern, while also calling on demonstrators to protest peacefully.
The clashes, pitting protesters opposed to the reforms against riot police and pro-government groups such as the Sandinista Youth, have rocked the capital, Managua, and half a dozen other cities over the last three days.
Some demonstrators carried heavy sticks or threw rocks as they faced off against armoured officers with batons and riot shields. One agent was wounded in the leg by a makeshift mortar on Friday in the capital.
Security forces have seized vehicles carrying provisions for the protesters, and at one point police invaded an area near Managua's Metropolitan Cathedral where the Roman Catholic Church had been collecting donations.
In response, protesters burned one of the famous "tree of life" sculptures that Mr Ortega's government has erected along numerous streets in the city.
A prominent umbrella organisation for Nicaraguan chambers of commerce condemned the violence, called for a peaceful march on Monday and urged authorities to respect freedom of expression.
Vice president, first lady and government spokeswoman Rosario Murillo alleged that violent acts by government supporters were provoked by those opposing the reforms, who she said were in turn being "manipulated" by political interests seeking to take advantage of the crisis.
"These moments are tragic and painful for all our people, for the entire country," Ms Murillo said.
The government said at least 28 police officers have been wounded in the violence, but has not released numbers of protesters hurt or arrested.
The demonstrations come after years in which the opposition claimed electoral fraud by the government, but without street protests reaching such magnitude or intensity.
"This is the release of a series of troubles that have been building among the people," sociologist and analyst Melvin Sotelo said, "and social security is the drop that overflowed the glass."
The government reforms increase income and payroll taxes and make changes to pensions to try to shore up Nicaragua's troubled social security system.