Ukrainian President Volodymyr Zelenskyy in an interview to AFP on Friday said that the ground assault launched by Moscow last week in the Kharkiv region could only be Russia's first step in a new offensive.

Zelenskyy also said his army needed more men to boost the forces' morale, a rare acknowledgement from the Ukrainian leader.

"We need to staff the reserves... A large number of (brigades) are empty. We need to do this so that the guys have a normal rotation. Then their morale will be improved," Zelenskyy told AFP.