GENEVA, Switzerland: Matilda Bogner, head of the United Nations human rights monitoring mission in Ukraine, has warned that the number of civilian deaths in Ukraine is thousands higher than the official figure of 3,381, with fatalities in the port city of Mariupol alone adding significantly to the total.

During a press briefing in Geneva, Bogner said, "We have been working on estimates, but all I can say for now is that it is thousands higher than the numbers we have currently given to you."

"The big black hole is really Mariupol, where it has been difficult for us to fully access and to get fully corroborated information," she added.

The warning came as the UN migration agency said 8 million people were internally displaced within Ukraine by the conflict.

Officials also said that dozens of additional bodies were discovered in Izium, Kharkiv region.

In a social media message announcing the deaths, Oleh Synehubov, head of Kharkiv's regional administration, said, "This is another horrible war crime of the Russian occupiers against the civilian population."

The latest phase of the war seemed to have settled into a grim back and forth struggle over villages and small towns destroyed by shelling, as both Ukrainian and Russian military officials claimed advances in the battle for the country's south and east, dominated by a 300-mile-long frontline.

While assessments by western defense and intelligence officials, as well as military analysts, focused on Russia's operational failures and heavy losses in men and equipment, there is little evidence of an end in sight for Moscow's invasion.