A Kremlin spokeswoman confirmed Mr Medvedev had approved the amendments, after they were announced in early November and pushed through the national Parliament and all 83 regional assemblies in less than two months.

Analysts have speculated the changes could be designed to pave the way for a return to the presidency by Prime Minister Vladimir Putin, who left the Kremlin in May but is often viewed as continuing to wield true power in Russia.

Last month, the Vedomosti daily newspaper cited two Kremlin sources saying Mr Medvedev would resign soon after the approval of the amendments and that Mr Putin would then run in a presidential election in 2009.

Critics have criticised lawmakers' haste in approving the amendments, which are the first change to Russia's post-Soviet constitution since its adoption under former president Boris Yeltsin in 1993.

The amendments sailed easily through both houses of the national Parliament, dominated by United Russia, a pro-Kremlin political party whose chairman is Mr Putin.

Only members of the opposition Communist Party, which has a minority in the Parliament, voted against the changes. Communists have complained the changes are part of an ''authoritarian'' trend in Russia.

The United Civil Front, an organisation led by former chess champion and bitter Kremlin critic Garry Kasparov, said after the parliamentary vote the changes would ''establish a dictatorial regime in Russia''.

Mr Medvedev, who took over from Mr Putin in May last year, has argued that the amendments will improve political stability.

He has said the changes would not apply to his current term, due to last until 2012, and would only affect the winner of the next election.

The amendments also extend parliamentary terms from the current four years to five and include a provision for the government to report to Parliament on a regular basis. The changes still need to be published in an official government newspaper to come into force. AFP