KYIV (Reuters) - Russia's choice of an economist as its new defence minister shows how far Moscow is preparing to go to overhaul its economy to serve its war needs, Ukrainian presidential adviser Mykhailo Podolyak said on Monday.

More than two years after Russia invaded Ukraine, Russian President Vladimir Putin named Andrei Belousov - a 65-year-old former deputy prime minister who specialises in economics - as his surprise new choice for defence minister on Sunday.

Putin also wants former defence minister Sergei Shoigu to become the secretary of Russia's powerful Security Council and to have responsibilities for the military-industrial complex, the Kremlin said.

"Russia is moving almost its entire economy onto military lines. It will be a militaristic country and its economy will be built exclusively to produce for the military," Podolyak told Reuters.

"Without a doubt these changes that we see today, they are evidence of the complete transformation of the Russian Federation," Podolyak said.

With Ukraine outgunned and outmanned on the battlefield, Russian forces are slowly advancing in the eastern Donbas region and pressing a new assault in the northeastern Kharkiv region.

Podolyak said the war was at a crucial stage after 27 months of the fighting, and called for tighter sanctions on Russia.

He also reiterated Kyiv's appeal for more Western military support.

Ukraine needed more air power, "more long-range capabilities, more ammunition and shells, because it is such a defining phase of the war that will determine the post-war world," he added.

(Reporting by Olena Harmash; Editing by Andrew Heavens)