By Geoffrey Smith

Investing.com -- Russian President Vladimir Putin declared a partial mobilization of the country's 2-million-strong military reserve and confirmed his intention to annex those parts of Ukraine currently under Russian occupation.

The move marks a massive shift for the Kremlin that risks antagonizing a large part of the Russian population and alienating what remains of his international support. Putin's invasion of Ukraine seven months ago has failed to achieve any of its strategic objectives and has sustained increasingly heavy losses of men and equipment in recent weeks as Ukrainian forces have recaptured important territory in the east of the country.

In a recorded video address, Putin said he "supports" the referenda on joining Russia that will be held on September 23rd - September 27th in the Kherson and Zaporizhzhya regions as well as the so-called Donetsk and Luhansk People's Republics, two puppet states set up by Russia in 2014. The votes repeat a playbook used by Russia to justify its annexation of Crimea in 2014, an act that has been recognized by only a handful of other states, including Syria, Nicaragua and Cuba.

Putin also made a thinly-veiled threat to use the country's nuclear arsenal to defend his conquests in Ukraine, at the same time accusing the West of practicing "nuclear blackmail" against it.

"If Russia’s territorial integrity is threatened we will use all means at its disposal. This is not a bluff," Putin said.

The announcement, which was delayed from Tuesday evening, is a response to recent defeats on the battlefield in Ukraine and signs that its leverage over European energy markets - which it has used to pressure Europe into abandoning its support for Ukraine - may be fading. European gas prices have fallen by around half from their peak in August, when gas monopoly Gazprom (MCX:GAZP) all but stopped deliveries to the continent.

Russia's military reserve was estimated by the International Institute for Strategic Studies at over 2 million in a book published last year. However, Defense Minister Sergey Shoigu said in a subsequent televised address that it would only affect 300,000 people.

Putin said the mobilization would be limited to those who have already served in the armed forces, and who have relevant experience and training. Even so, the announcement sparked immediate calls for protests on social media.

"Thousands of Russian men - our fathers, brothers and husbands - will be thrown into the meat-grinder of war," the self-styled democratic youth movement Vesna (Spring) said in a statement. "For what are they going to die?"