``In the direction of Kharkiv, Russian army units are regrouping and trying to prevent the further advance of our troops in the direction of the state border of Ukraine,'' defense ministry spokesman Oleksandr Motuzyanyk said in his regular media briefing.

``To this end, the occupiers launch unceasing artillery attacks on our troop units in order to inflict human losses, as well as to damage weapons and military equipment,'' Motuzyanyk added.

He did not clarify how close Ukrainian forces were to the border.

According to the defense ministry briefing, Moscow's troops were opening fire ``along the entire line of confrontation'' in Ukraine's east, and attempting to penetrate Ukrainian defenses.

Also on Thursday, the Ukrainian military's General Staff said in its daily operational statement that Russian forces continued their attempts to storm several cities in Ukraine's industrial heartland of Donbas that day, but had no success.