MOSCOW (AFP, REUTERS) - Russian lawmakers will begin reviewing President Vladimir Putin's nomination of a little-known tax chief as the new prime minister on Thursday (Jan 16) after his announcement of a sweeping constitutional shake-up fuelled speculation about his future plans.

Russia's ruling party, United Russia, unanimously approved Mikhail Mishustin's candidacy as prime minister ahead of a formal parliamentary vote, Anastasia Kashevarova, an aide to parliament's speaker said on social media.

The overwhelmingly Kremlin-loyal State Duma lower Parliament is likely to approve Mr Mishustin for the role, following the shock resignation of the government in the wake of Mr Putin's call for reforms to reshape Russia's political system.

The series of bombshell announcements made during and after Mr Putin's state of the nation speech triggered speculation about his role past 2024, when his current presidential term expires.

Some suggested that 67-year-old Mr Putin, who is currently two years into his fourth presidential term and has steered the country since 1999, could be laying the groundwork to assume a new post or remain in a powerful behind-the-scenes role.

It is also unclear whether Mr Mishustin, a relatively obscure technocrat disengaged from political debate whose recent career revolved around Russia's tax service, is a temporary figure or could be groomed as Mr Putin's successor.

The State Duma said on its website that Mr Mishustin will hold "consultations" with the four parties represented in Parliament prior to the plenary session starting at 10am (0700 GMT), during which his candidacy will be formally reviewed.

'STAYING NUMBER ONE'?

In his state of the nation speech, Mr Putin said he wanted more authority transferred to Parliament from the president, including the power to choose the prime minister and senior Cabinet members.

Outlining the proposals, which would be the first significant changes to the country's Constitution since it was adopted in 1993, Mr Putin noted the "demand for change" among Russians.

Frustration has been building in Russia, where ordinary people have seen their incomes stagnate or decrease for five years, while a key reform hiking the pension age has led to anger and a fall in Mr Putin's ratings.

Mr Dmitry Medvedev, prime minister since 2012, announced the resignation of his government soon after Mr Putin's speech on Wednesday, saying that the constitutional proposals would make significant changes to the country's balance of power.

He remains acting prime minister until a new head of government takes the reins.

Independent political analyst Maria Lipman said all of the announced changes indicate that Mr Putin wants to "stay on as No. 1 in the country, without any competitors".

She said he could be deliberately weakening the presidency before relinquishing the role.

Russia's opposition also said the proposals indicate Mr Putin's desire to stay in power.

"To remain the sole leader for life, who took over the whole country as his property... is the only goal for Putin," tweeted opposition leader Alexei Navalny.

If 53-year-old Mishustin is appointed, he would have a week to propose a new government and ministers.

The former head of an investment group trained as an engineer has a PhD in economics and has led Russia's Federal Tax Service since 2010.

He also shares Mr Putin's love for hockey and has been seen at matches with security services officials, according to reports.

Former opposition lawmaker Gennadiy Gudkov called Mr Mishustin "a new faceless functionary without ambition" who embodies a system that is "detrimental for the economy".

Mr Medvedev - who also served as Russian president for four years from 2008 - is expected to stay close to the Russian leader, transitioning to a role as deputy head of the country's Security Council, which Mr Putin chairs.

"He remains what he's always been: (Putin's) alter ego," tweeted head of Carnegie Moscow Centre Dmitry Trenin, suggesting that Mr Medvedev could be being groomed as the next president.