(CNN) The United Nations said Friday that it has video evidence appearing to show Iranian security forces "shooting to kill" protesters during Iran's latest wave of demonstrations.
In a statement on Friday, UN High Commissioner for Human Rights Michelle Bachelet said she was alarmed by "the continuing lack of transparency about casualties and the treatment of thousands of detainees" during the recent protests in Iran.
Bachelet said "prompt, independent and impartial investigations" into all possible violations needed to be undertaken, "including the killing of protesters."
Iranians took to the streets in mid-November, shortly after the government announced an increase in fuel prices by as much as 300%. The exact death toll in the protests remains unclear as the government has withheld these numbers.
The UN Human Rights Office said it had information suggesting that at least 208 people were killed, including 13 women and 12 children. It said at least 7,000 have reportedly been arrested across the country. The government imposed a nationwide internet shutdown for over a week.
"Verified video footage indicates severe violence was used against protesters, including armed members of security forces shooting from the roof of a justice department building in one city, and from helicopters in another," Bachelet said.
Her office had received footage appearing to show security forces shooting unarmed demonstrators from behind while they were running away, and shooting others directly in the face and vital organs -- "in other words, shooting to kill," she said.
"These are clear violations of international norms and standards on the use of force, and serious violations of human rights," Bachelet said. "In such circumstances, with so many reported deaths, it is essential the authorities act with far greater transparency."
"All in all, the picture now emerging from Iran is extremely disturbing," Bachelet added.
While the UN Human Rights Office and watchdog Amnesty International say at least 208 people have been killed, the government hasn't released an official number.
Iran's Supreme Leader Ayatollah Seyyed Ali Khamenei said in a speech in November that "several" people had died in the protests.
Khamenei blamed opponents and foreign enemies for "sabotage," according to Reuters, quoting state television. "The counter-revolution and Iran's enemies have always supported sabotage and breaches of security and continue to do so," he said.
More than 1,000 protesters have been arrested across the country, according to the semi-official Fars News Agency. However, the UN said the number is much higher -- with at least 7,000 reportedly arrested across the country.
Iran's supreme leader has said that he supported the government's decision to raise gas prices, according to state-run Press TV, but he urged officials not to increase the price of other commodities.
The White House said in a statement in November that the US is supporting "the Iranian people in their peaceful protests against the regime that is supposed to lead them."
"We condemn the lethal force and severe communications restrictions used against demonstrators," the statement said.
"Tehran has fanatically pursued nuclear weapons and missile programs, and supported terrorism, turning a proud nation into another cautionary tale of what happens when a ruling class abandons its people and embarks on a crusade for personal power and riches," it added.
Nearly two years ago, in another wave of protests, people took to the streets to demand better living standards. At least 22 people died in those protests, according to Iranian officials.