Russia and Ukraine rarely communicate on the total number of troops involved in the conflict, or on their respective losses.

"Forty-five thousand Muscovites are fighting in the area of the special military operation," Sobyanin was cited as saying by Russia news agency Interfax.

The mayor added they represented a "considerable part" of the fighters there.

Among them, "at least 5,000 people are professional soldiers," he also said.

Beginning August, Deputy Security Council Chairman Dmitry Medvedev said Russia had enlisted over 230,000 additional personnel into the army since the start of the year.

Last September, President Vladimir Putin announced a "partial" military mobilisation of 300,000 men to replenish the troops.

The announcement -- Russia's first such mobilisation since World War II -- sent shock through across the country as thousands of men were drafted into the army.

Unwilling to announce a second mobilisation drive, Moscow has since opted for a massive PR campaign, hoping to lure Russians with financial incentives.

Defence Minister Sergei Shoigu said last year the size of Russia's army would be increased to 1.5 million people, as Moscow presses ahead with its offensive in Ukraine.