Ukraine's President Volodymyr Zelenskyy says Russia's cross-border attacks on the Kharkiv region in the country's east are aimed at spreading Ukrainian forces thin as intense fighting continues in the Donetsk region.

Zelenskyy made the remark in footage released on Sunday.

He said intense combat operations are underway on multiple fronts in Donetsk in addition to the battles in Kharkiv. He acknowledged the difficulty for Ukraine but said it will deter Russian assaults.

The Russian forces that crossed the border from the north are stepping up operations in Kharkiv. Russia's defense ministry said on Sunday they captured four more settlements.

The governor of the Kharkiv region said on the same day that Russian attacks were continuing day and night in the region's north.

The governor said two civilians were killed, and during the past two days about 4,000 residents evacuated.

The western Russian region of Belgorod borders Ukraine. Its governor said on Sunday that Ukrainian forces shelled a 10-story apartment in the regional capital, killing at least eight people.

Ukraine has denied involvement, saying the accusations are aimed at justifying further attacks by Russia.