"The Russian Federation has concentrated more than 420,000 servicemen in our territories that are temporarily occupied, including Crimea," Skibitsky said at a conference in Kyiv.

The figure "does not include the Russian National Guard and other special units that maintain occupation authorities on our territories," he added.

Skibitsky also said Russia had for a month been actively launching attacks from Crimea, which it annexed in 2014.

"Drones deployed in Crimea are used against our ports of Izmail and Reni," which have been used as alternative exports hub, particularly since the expiry of a deal protecting exports on the Black Sea.

Ukraine launched a counteroffensive in the east and south in June but has come up against fierce resistance from entrenched Russian forces.

Kyiv's troops are also contending with renewed assaults around Kharkiv in the northeast, in areas liberated last year.

"(Russians) want to take their revenge" in the Kharkiv region, said Deputy Defence Minister Ganna Malyar.

She said Russian troops were trying to disperse Ukrainian forces in the east "so that we can't centralise them around Bakhmut, where we are successfully advancing."

She acknowledged that "the enemy is strong, they have more people and weaponry."

Malyar said the Russian army fired "almost 400,000 shells" at Ukrainian positions on the eastern front over the past week.

ant-brw /pvh