Russia has announced the implementation of martial law in the four regions of Ukraine that it claimed to annex last month.

Russian President Vladimir Putin announced Wednesday that the regions of Kherson, Zaporizhzhia, Luhansk, and Donetsk in Ukraine were being placed under martial law.

Putin didn't immediately spell out the steps that would be taken under martial law, but said his order was effective starting Thursday. His decree gives law enforcement agencies three days to submit specific proposals and orders the creation of territorial defense forces in the four annexed regions.

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"We are working to solve very difficult large-scale tasks to ensure Russia’s security and safe future, to protect our people," Putin said in televised remarks at the start of a Security Council meeting. "Those who are on the frontlines or undergoing training at firing ranges and training centers should feel our support and know that they have our big, great country and unified people behind their back."

Russia has responded to the explosion on the Crimea bridge with a brutal bombing campaign that has targeted population centers, parks and infrastructure as Ukraine's cold winter approaches.

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Russian drone and missile attacks have destroyed nearly a third of Ukraine's power stations, but Ukrainian forces continue to gain ground President Volodymyr Zelenskyy announced Tuesday.

Putin announced the annexations in September, claiming it was the "will of millions" after referendums in the regions that the West have labeled a "sham."

Fox News' Anders Hagstrom and the Associated Press contributed to this report.