Moscow  - Russia's upper house of parliament on Wednesday approved a Kremlin bill to lengthen the presidential term from four to six years.

The bill to amend the constitution was backed by 144 senators, a majority in the Federation Council. Only one senator voted against.

The Kremlin-sponsored reform was near-unanimously voted through Russia's lower house, the State Duma, on Friday.

The proposal now faces one last vote, where it must be approved by two thirds of Russia's regional legislatures - most of are dominated by pro-Kremlin party United Russia - to become law.

If passed, it would be the first change to Russia's constitution since the document was drafted 15 years ago after the collapse of the Soviet Union.

"With the highest probability - 99.9 per cent - the constitutional amendments will be adopted and enter into force before the end of the year," Federation Council chairman Sergei Mironov told news agency Itar-tass after the vote Wednesday.

While President Dmitry Medvedev launched the draft law just six months into his presidency, constitutional experts say the amendment would not apply to him.

Many analysts say he is more likely a stand-in for Putin to return to the Kremlin for what would now be 12 more years.

Putin stepped down as president in May because the constitution barred him from running for a third consecutive term.

Now serving as prime minister, Putin has not ruled out a return to the Kremlin office. He backed the term extensions last week, though he said it was "premature" to name who they might benefit.

Meanwhile, opposition activists Wednesday staged a one-man picket outside the chambers of the upper house, in order to circumvent regulations banning larger assemblies.

The vote came a little over two weeks after Medvedev declared his intention to push through the amendment in his state-of-the-nation address on November 5.

A survey by state-run pollsters VTsIOM released Friday found 56 per cent of Russians in favour of a longer presidency and 29 per cent opposed. (dpa)