A Ukrainian official said 70 Ukrainian soldiers were killed in a Russian artillery attack on a military base Monday.
Dmytro Zhyvytskyy, governor of the Sumy region, posted the death toll on Facebook after a shelling attack by Russian forces, Reuters reported.
The attack took place in the town of Okhtyrka, according to Zhyvytskyy.
Fighting on Sunday in the region also led to multiple civilians and Russian soldiers dying, he added in the post, The Associated Press reported.
Fighting in Ukraine has intensified as Russia’s invasion enters its sixth day, with the U.N. saying at least 136 Ukrainian civilians have been killed, although the true total is likely much higher.
The U.N. human rights office said many of the deaths are coming from airstrikes and shelling from heavy artillery and multiple launch rocket systems.
Ukrainian President Volodymyr Zelensky has called for a war crimes investigation into Russia, accusing Moscow of intentionally striking civilian targets, accusations Russia has denied.
U.S. intelligence says Ukrainian resistance to the invasion is stronger than expected as Ukraine still has control of its capital city of Kyiv.
However, there is also mounting concern that Russia will intensify its attacks as President Vladimir Putin becomes increasingly frustrated with Ukraine’s resistance.