KYIV, March 27 - Ukrainian defense officials said on Sunday that some Russian military units have returned to Belarus through Chernobyl to regroup amid mounting losses as Moscow's invasion enters its fifth week.

In a statement on Saturday, General Staff of the Armed Forces of Ukraine (GSAFU) said an unspecified number of Russian forces have left Ukraine and crossed into Belarus. It added that the units could return to bolster attempts to encircle the capital Kyiv.

"Several units have been taken to the Chernobyl district with further relocation to the territory of the Republic of Belarus to hold measures for the restoration of armour," GSAFU said in its Facebook post.

"It is not excluded that after specified measures, regrouping and strengthening the grouping of the occupiers, action on blocking Kiev from the south-west direction will be restored," it added.

Fighting continued around Kyiv over the weekend. According to the New York Times, Russian forces shelled Boyarka, a town outside of the capital, on Saturday.

Boyarka mayor Oleksandr Zarubiv told the newspaper that five residents were hospitalized from the incident.

"Russia can plan its attacks on us but we are also getting ready and I can say that it will not be easy for them here," Zarubiv said.

GSAFU added that it was able to halt Russian military movement toward the town of Brovary, adding that Russian forces in the area are now on the defensive.

"In the direction of Brovary, the opponent's units are stopped. The enemy was forced to move to defense, carrying out engineering equipment positions," GSAFU said, adding that Russian forces "suffered significant losses." (yn/ez)