(CNN) Protesters and police clashed once again in the Chilean capital of Santiago on Thursday, as authorities extended a curfew for the sixth consecutive night. An apology from President Sebastian Pinera failed to temper escalating levels of violence on the streets, which have so far led to at least 18 deaths.
The United Nations human rights council plans to send a special mission to investigate allegations of rights abuses in the South American country amid a week of deadly clashes between protesters and police, UN human rights chief and former Chilean president Michelle Bachelet said Thursday.
Protests have paralyzed parts of the capital city for seven days in a row and Chilean police have responded to demonstrators by firing tear gas, rubber bullets, and water cannons.
In a national televised address Tuesday night, Pinera apologized for "decades" of accumulated problems and announced a new social and economic agenda in the wake of the deadly unrest.
"It's true -- problems have not occurred in recent days. They have been accumulating for decades," he said of the South American country of 18 million people.
The President promised social and economic reforms to tackle issues at the heart of the unrest, including pension raises, affordable medical insurance, lowering the prices of medicines and stabilizing electricity prices.
Tensions escalated Wednesday when a four-year-old child was killed after a person driving an unidentified vehicle rammed into a crowd in the city of San Pedro de la Paz. One other person died in the incident.
A third person was killed Wednesday after being attacked by Chilean police in Santiago, Interior Undersecretary Rodrigo Ubilla told reporters.
The three deaths raised the confirmed death toll from the protests to 18.
Pinera's address has done little to calm the protests, which began over a now-suspended price hike for subway tickets in Santiago but have since expanded, revealing deep-seated anger among ordinary Chileans who feel they have been excluded from the nation's economic rise.
Many are frustrated over economic inequalities, living costs and rising debt in a country that remains among the most prosperous and stable in Latin America.
The government has extended a curfew for the Santiago metropolitan region for a fifth consecutive day. Classes and schools in the city have also been suspended until Friday.
The curfew began at 10 p.m. local time (9 p.m. ET) Wednesday and will end at 4 a.m. (3 a.m. ET) Thursday, "limiting citizens mobility in order to guarantee the tranquility and order in the area," according to a Twitter statement from the Head of the National Defense.
In his address, Pinera stressed the importance of peace and told Chileans that the government will lift the curfew when public order and tranquility are restored.
While much of the protesters have been peaceful, there has been widespread vandalism, looting and arson of shops, business and metro stations. The corporate headquarters of a utility company in downtown Santiago were firebombed Friday, and on Saturday, in the port city of Valparaiso, the offices of the country's oldest newspaper, Mercurio were torched, Reuters reported.
Several cities in the country have been placed under a state of emergency as thousands have taken to the streets. The government deployed the military to put down the unrest -- the first time since Gen. Augusto Pinochet's 17-year military dictatorship ended in 1990.
Human Rights Watch has called on the government to investigate crimes committed by demonstrators as well as security forces who responded with excessive force.
"We are deeply concerned by the images of instances of police brutality coming out of Chile," said Jose Miguel Vivanco, Americas director at Human Rights Watch. "President Pinera should make clear to Chilean security forces that they need to respect human rights and ensure that agents implicated in abuses are promptly and impartially investigated."
Chile is one of Latin America's wealthiest countries, but it also has one of highest levels of income inequality in the world.
Almost a third of Chilean workers are employed in informal or non-permanent jobs, and one in two Chileans has low literacy skills, according to the OECD.