The human toll of the invasion of Ukraine is becoming ever more apparent as Russian troops pull out of the region of the nation's capital Kyiv.

The governor of the Sumy region, northeast of the capital, said through social media that hundreds of civilians have been killed.

In a Telegram post, Sumy Governor Dmytro Zhyvytskyi confirmed that Russian forces had begun withdrawing from the region and hundreds of civilians have been killed. The post strongly condemns Russians for what the governor describes as unprecedented acts of cruelty.

This follows reports by Reuters and others that the bodies of hundreds of civilians had been abandoned on the streets of Bucha, northwest of Kyiv.

Ukraine's Prosecutor General Iryna Venediktova said on Sunday that the bodies of 410 civilians had been transported out of towns near Kyiv. She condemned the Russian invading forces, describing the corpses as a smoking gun showing that Russia had committed war crimes. Moscow denies such allegations.

Analysis by Britain' defense ministry suggests that the city of Mariupol on Ukraine's Black Sea coast is a key objective of Russian forces. If the invaders can take the port city it will provide a land corridor from Russia to the occupied territory of Crimea.

The ministry also said Moscow has deployed troops, including mercenaries from the private Wagner Group company, to eastern Ukraine as part of a regrouping of personnel in the east of the country.

Some fear that the number of civilian casualties may rise further, as Russian advances in the east could intensify fighting.

Negotiators from Ukraine and Russia are set to resume ceasefire talks on Monday. It is not certain the negotiations will lead to a breakthrough, with Moscow remaining negative about an early end to the fighting.