MOSCOW (AP) — President Vladimir Putin engineered a surprise shake-up of Russia’s leadership Wednesday, proposing changes to the constitution that could keep him in power well past the end of his term in 2024.

Hours after he made the proposals, Prime Minister Dmitry Medvedev resigned and Putin named the little-known head of Russia’s tax service to replace him.

Putin kept his longtime ally Medvedev in the Kremlin’s leadership structure by appointing him to the newly created post of deputy head of the presidential Security Council. But the duties and influence of that position are unclear.

The shakeup sent shock waves through Russia’s political elites who were left pondering what Putin’s intentions were and speculating about future Cabinet appointments.

Putin’s proposed constitutional reforms, announced in a state of the nation address, indicated he was working to carve out a new governing position for himself after his term ends, although the suggested changes don’t immediately specify what path he will take to stay in charge.

The 67-year-old former KGB operative, who has led Russia for more than 20 years, often keeps his intentions secret until the very last moment.

Alexei Navalny, the most prominent Russian opposition leader, tweeted that Putin’s speech clearly signaled his desire to continue calling the shots even after his presidential term ends.

“The only goal of Putin and his regime is to stay in charge for life, having the entire country as his personal asset and seizing its riches for himself and his friends,” Navalny said.

Independent analyst Masha Lipman told The Associated Press: “The goal is for the system to remain stable and for Putin to retain his grip on power and to remain what he has been throughout these 20 years — the most important politician in the country, the ultimate decision-maker, the uncontested unchallenged leader of no alternative.”

The Kremlin said Tax Service chief Mikhail Mishustin was nominated to replace Medvedev, who has been prime minister for nearly eight years. Approval by the Duma on Thursday is virtually certain.

Mishustin has no political experience, indicating he will dutifully carry out the Kremlin’s wishes as head of the Cabinet.

He is credited with modernizing Russia’s tax system. Analyst Gleb Pavlovsky, a former Putin adviser, told the Interfax news agency that Mishustin is “a splendid bureaucrat, in the best sense of the word.”

The move is the third time in the Putin era that major leadership changes have come suddenly from the top. Putin came to power in the first one, when he became acting president after Boris Yeltsin’s surprise resignation on New Year’s Eve 1999.

In 2007, as his second term neared its end, he anointed Medvedev to succeed him. Medvedev then said Putin should be prime minister — moves that critics decried as an imposed job-swap without input from the electorate. Medvedev was president in 2008-12, but Putin, as premier, appeared to be effectively in charge.