(Adds Ukraine presidential adviser comments on south, Kherson details)
July 27 (Reuters) - Russian forces are undertaking a "massive redeployment" of troops to three southern regions of Ukraine in what appears to be a change of tactics by Moscow, a senior adviser to President Volodymyr Zelenskiy said on Wednesday.
Russian forces have taken over Ukraine's second biggest power plant, presidential adviser Oleksiy Arestovych said in an interview posted on YouTube. Russian-backed forces had earlier announced the capture of the Soviet-era, coal-fired Vuhlehirsk plant in eastern Ukraine.
"They achieved a tiny tactical advantage - they captured Vuhlehirsk," Arestovych said.
Arestovych said Russia seemed to be switching from offence to a strategic defence, using tactical attacks in a bid to weaken Ukraine's offensive potential in the crucial eastern Donetsk industrial region.
"(This would) place us in a position where we are unable to liberate all our territory and call for talks," he said.
Ukraine has made clear it intends to recapture the southern city of Kherson, which fell to Russia in the early days of the war.
Oleksiy Danilov, secretary of Ukraine's National Security and Defence Council, earlier tweeted that Russia was concentrating "the maximum number of troops" in the direction of the Kherson but gave no details.
Arestovych said Russia was also sending troops to the Melitopol and Zaporizhzhia regions in the south.
Ukraine has shelled an important bridge straddling the Dnipro river in Kherson, closing it to traffic. Russian officials had earlier said they would turn instead to pontoon bridges and ferries to get forces across the river. (Reporting by David Ljunggren and Ronald Popeski; Editing by Grant McCool)