The bill was announced only last week by President Dmitry Medvedev and is being fast-tracked through parliament.

Mr Putin became prime minister this year after being obliged under the constitution to step down after two consecutive presidential terms.

But speculation is rife that he is planning to return to the presidency.

The BBC's Richard Galpin says it has always been assumed that Mr Putin may return after Mr Medvedev has completed one term.

But the apparent rush to get this constitutional amendment through is being seen by some as a sign that Mr Putin is in a hurry and may return much sooner.