MOSCOW (AFP) — President Vladimir Putin on Wednesday ordered "partial" mobilization in Russia, in an escalation of what Moscow calls its military operation in pro-Western Ukraine.

"I consider it necessary to support the proposal of the Defense Ministry and of the General Staff to conduct partial mobilization in the Russian Federation," Putin said during a televised address to the nation.

He added that a relevant decree has already been signed and will come into force on Wednesday.

Putin said that Russia will use all available means to protect its territory, accusing the West of seeking to "weaken, divide and ultimately destroy our country."

"When the territorial integrity of our country is threatened, we will certainly use all the means at our disposal to protect Russia and our people. This is not a bluff," Putin said.

"Those who are trying to blackmail us with nuclear weapons should know that the wind can also turn in their direction," Putin added.

The mobilization is a "sign of weakness, failure," the United States ambassador to Ukraine remarked.

"Sham referenda and mobilization are signs of weakness, of Russian failure," Bridget Brink wrote in a a Twitter message.

"The United States will never recognize Russia's claim to purportedly annexed Ukrainian territory, and we will continue to stand with Ukraine for as long as it takes," she said.

Meanwhile, Russia's Defense Minister Sergei Shoigu said Wednesday that 5,937 Russian soldiers have died in Ukraine since the February military intervention, in a rare admission of military losses from Moscow.

"Our losses for today are 5,937 dead," Shoigu said in televised remarks, adding that Russia is "fighting not so much Ukraine as the collective West" in Ukraine.

Nuclear plant shelled

The Ukrainian nuclear operator Energoatom on Wednesday accused Russia of again striking the Zaporizhzhia atomic power plant in southern Ukraine.

The strike damaged a power line at the plant causing the stoppage of several transformers of the number six reactor and forcing a brief launch of emergency generators, Energoatom said.

"Russian terrorists shelled the Zaporizhzhia nuclear power plant again" during the night, Energoatom said on Telegram.

But radiation remained "at the normal background values level" said the plant on Telegram.

"Emissions and discharges of radioactive substances into the environment do not exceed the established permissible values," it said.

Energoatom called on the International Atomic Energy Agency for "more resolute actions" against Moscow.

Even "the presence of IAEA inspectors does not stop" the Russians, it said.

Europe's largest atomic facility, located in Russian-held territory in Ukraine, has become a hot spot for concerns after tit-for-tat claims of attacks there.

The plant was seized by Russian troops in March and shelling around the facility has spurred calls from Kyiv and its Western allies to de-militarize areas around nuclear facilities in Ukraine.

Early in the war there was fighting around Chernobyl in the north, where an explosion in 1986 left swathes of the surrounding territory contaminated.

French President Emmanuel Macron this month urged his Russian counterpart Putin to withdraw heavy weapons from the Zaporizhzhia region, while the Russian leader cautioned against the potential "catastrophic" consequences of fighting there.

A monitoring team of the IAEA deployed there in early September.

Russia was accused Monday of bombing a third nuclear plant site, the Pivdennoukrainsk plant in the southern Mykolaiv region.

Moscow is stepping up "nuclear blackmail," the plant's director said after the strike caused a large crater seen by AFP journalists hundreds of meters from the plant.