Medvedev gave final approval to the measure after a hurried legislative drive that lasted less than two months, ignoring complaints by the opposition that parliament is legally required to wait a year before ratifying any change to the constitution.

The extension of the presidential term is the first substantive amendment to Russia's post-Soviet constitution since it was adopted in 1993. The speed with which the Kremlin pushed the measure through parliament and the nation's provincial legislatures has prompted widespread speculation that Putin is planning to return to the presidency, perhaps as soon as next year.

After serving two terms as president, Putin stepped aside this year because he was constitutionally barred from a third consecutive term. He engineered the election of his protege, Medvedev, who then appointed him prime minister. With Russia facing its worst economic crisis in a decade, though, analysts say Putin may have concluded he would be better shielded from rising public discontent if Medvedev resigned and allowed him to return to the presidency for a new six-year term.