More than 8,000 civilians have been recorded killed in Ukraine since Russia invaded nearly a year ago, the U.N. human rights office said on Tuesday, describing the figure as only the "tip of the iceberg" with thousands more thought to have died.

The latest toll represents a significant upward revision from the previous tally, released earlier this month, of 7,199 recorded killed since the start of Moscow's full-scale invasion on Feb. 24, 2022. Around 90% of the victims were killed by explosive weapons, it added.

"Our data are only the tip of the iceberg. The toll on civilians is unbearable," U.N. High Commissioner for Human Rights Volker Turk said in a statement.

Matilda Bogner, head of United Nations Human Rights Mission in Ukraine, said it believes thousands of civilian deaths remained to be counted, many of them in the southern Ukrainian city of Mariupol, now under Russian control.

The U.N. tally includes 2,000 civilian deaths in Mariupol, which was home to around 450,000 people before Russia laid siege to it for three months and blasted it to the ground.

"We have uncorroborated information indicating that the numbers are thousands higher than we have documented and a huge number of those are from Mariupol," Bogner told reporters.

Russia denies intentionally targeting civilians in what it calls a "special military operation."