The organization said he died after a police vehicle ran him over twice but Tunisia's Ministry of Interior said that he had suffocated to death from tear gas because he had a chronic respiratory condition.
Chibani reported that 97 security officers were injured in this week's violence, with dozens of police cars damaged.
In a written statement, Rupert Colville, spokesperson for the Office of the UN High Commissioner for Human Rights, said authorities must ensure that people are not arrested in an arbitrary manner and that their rights are respected.
"We're concerned about the high number of arrests, some 778 people we understand have now been arrested since Monday, and around a third of those arrested were between the ages of 15 and 20 so very young", Colville told reporters in Geneva.
The protests draw on anger over price and tax increases included in this year's budget that took effect on January 1.
Man kills mother during tantrum over video games, police say
Matthew Nicholson, 28, got in a fight with his mother Lydia Nicholson, 68, and shot her in the head, police said. . He allegedly grabbed a gun and shot his mother before his 81-year-old father wrestled away the firearm.
The unrest comes ahead of Sunday's seventh anniversary of the revolution that toppled the dictator Zine El Abidine Ben Ali in 2011, an event that sparked similar uprisings in Egypt, Libya, and Syria.
But frustration has grown among many Tunisians over economic stagnation and unemployment.
A new anti-austerity youth movement - named Fech Nestannow, which translates as "What are we waiting for?" - has sprung up since the start of the year and is seeking to rally opposition to the measures.
Last year, the Washington-based International Monetary Fund agreed a four-year loan program worth about $2.8 billion with Tunisia, tied to economic reforms.