WASHINGTON, June 15 (RIA Novosti) - A senior Kremlin official has said a successor for President Vladimir Putin, whose tenure expires next year, could be someone not widely considered as a potential candidate.

Two first deputy prime ministers and close associates of Putin, Sergei Ivanov and Dmitry Medvedev, are currently viewed as the most likely successors to the president.

Igor Shuvalov, speaking at a the Center for Strategic and International Studies in Washington, said: "People talk about two possible candidates, but the president could come up with another surprise, and perhaps later this year you could learn about another possible figure."

The current leader has presided over an economic and political revival in Russia following the turbulent 1990s, and has been pressed by supporters to stay on for a third term. Putin's backing will be of key importance for presidential contenders in the March 2008 elections.

Putin has so far refused to name his preferred successor. He has also pledged not to amend the Constitution to allow for a third term, but suggested that the presidential term could be extended to five or seven years in the future.

Shuvalov said Putin - criticized by opponents for clamping down on dissent - was not comparable to his counterparts in Belarus, Turkmenistan and other ex-Soviet states, who have willfully altered legislation to allow them to stay in power indefinitely.

"People ask all the time whether President Putin will really step down or whether he is considering amending the Constitution to stay on. We have heard him, even in private, say he will quit," the president's aide said.

Vladimir Putin has dismissed suggestions that he will appoint a successor, saying Russians will choose their next president in a free vote. Analysts have not ruled out that Putin will return as president in the 2012 elections.