(AFP) - Russia's widespread and indiscriminate attacks in Ukraine are of "immense concern", the UN rights chief said Wednesday, warning that they could amount to "war crimes".

Speaking before the UN Human Rights Council in Geneva, Michelle Bachelet said that the entire population of Ukraine had been "enduring a living nightmare" since Russia launched its full-scale invasion five weeks ago.

Presenting her latest report on the rights situation in the now war-ravaged country, Bachelet voiced particular concern over the "persistent use of explosive weapons with wide area effects in populated areas."

Bachelet said missiles, heavy artillery shells and rockets and airstrikes were causing "massive destruction and damage to civilian objects."

In addition, she said her office had received "credible allegations that Russian armed forces have used cluster munitions in populated areas at least 24 times".

The office was likewise probing allegations that Ukrainian forces had also used such weapons, she said.

- 'Massive destruction' -

"Homes and administrative buildings, hospitals and schools, water stations and electricity systems have not been spared," Bachelet said.

The UN rights office had verified 77 incidents in which medical facilities were damaged, including 50 hospitals, with 10 of the facilities completely destroyed, she said, stressing that the actual numbers are "likely to be considerably higher."

"Indiscriminate attacks are prohibited under international humanitarian law and may amount to war crimes," Bachelet warned.

"The massive destruction of civilian objects and the high number of civilian casualties strongly indicate that the fundamental principles of distinction, proportionality and precaution have not been sufficiently adhered to."

Ukrainian ambassador Yevheniia Filipenko meanwhile thanked Bachelet for describing "in appalling details the horrors of Russia's assault on Ukraine and the war crimes committed."

She hit out at Moscow's "vicious methods" and warned that Moscow's "flagrant violation of the UN Charter and fundamental principles of international law" would "have long-lasting implications for the future of the world order and humanity."

- 'Sheer terror' -

Bachelet said her office had verified 1,189 civilian deaths in Ukraine, including 98 children since February 24.

But she warned that the true toll was surely far higher, pointing out that her staff had little access to verify casualties in some of the hardest-hit areas.

Those include the besieged and devastated southern port city of Mariupol, where Bachelet said "people are living in sheer terror."

Russian forces have encircled the city and their steady and indiscriminate bombardment has killed at least 5,000 people, but possibly as many as 10,000, according to one senior Ukrainian official.

"Civilians are enduring immeasurable suffering, and the humanitarian crisis is critical," Bachelet said.

She also said her office was investigating claims that civilians in Mariupol had been "forcibly evacuated, either to territory controlled by Russian-affiliated armed groups or to the Russian Federation."

Filipenko charged that "an estimated 40,000 Ukrainian citizens have been trafficked in this way."

Representatives from a long line of countries chimed in to decry Russia's war in Ukraine.

US ambassador Michele Taylor slammed Russian President Vladimir Putin's "brutal, unprovoked and premeditated invasion."

"We are horrified by Russia's tactics," she told the council

"It is clear that President Putin is hell-bent on reducing Ukraine's towns and cities to dust," said British ambassador Simon Manley told the council, while EU ambassador Lotte Knudsen warned "Ukraine is becoming a full-scale humanitarian catastrophe."

Russia's representative Yaroslav Eremin meanwhile chose to counter-attack.

"We are extremely concerned with the mass violations of international humanitarian law and human rights by the Ukrainian military," he told the council, charging that Ukrainian militants were using civilians as "human shields."

© Agence France-Presse