Mikhail Gorbachev has warned that Russia "could lose six years" if Vladimir Putin returns to the presidency.
Putin, currently prime minister, looks set to return as Russia's president next year after current President Dmitry Medvedev proposed that his predecessor make another run for the country's top job. Putin, 58, and Medvedev, 46, have backed each other to essentially switch roles in 2012.
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But former Soviet Union leader Gorbachev said that serious changes are needed in Russia.
"We can assume that there will be no movement forward if there are not serious changes along the lines of a replacement of the entire system," Gorbachev wrote in the opposition Novaya Gazeta newspaper, which he partly owns, the BBC reports.
"Without this we could lose six years. I think that the future president needs to think about this very seriously."
Meanwhile, Medvedev told Finance Minister Alexei Kudrin on Monday to resign after Kudrin refused to serve in government if Medvedev became prime minister under the planned shuffle, Reuters reports.
Putin told a ruling United Russia party congress on Saturday he would stand again. He could in theory remain as president until 2024.
"I think it's right that the party congress support the candidacy of head of the government, Vladimir Putin, in the role of the country's president," Medvedev told thousands of cheering delegates at the congress on Saturday, the Guardian reports.
Putin was previously president from 2000 to 2008, but was barred by Russia's constitution from a third successive term in office, notes Reuters. He was replaced by Medvedev, but is still considered to wield more power.
"I want to thank you for the positive reaction to the proposal for me to stand for Russian president," Putin said following Medvedev's suggestion that he run for president, the BBC reports.
"For me this is a great honor," Putin said.
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