Russian President Vladimir Putin says he could run for a fourth presidential term in 2018. If he serves four terms, that would keep him in power for about a quarter century and make him the nation's longest-serving leader since Josef Stalin.

Putin, who served two consecutive four-year terms starting in 2000, became prime minister in 2008 to observe a constitutional limit of two consecutive terms.

Putin continued calling the shots as premier with his longtime ally, Dmitry Medvedev, serving as a placeholder. Medvedev initiated a law that extended the presidential term to six years, and Putin won a third term in 2012 despite major public protests in Moscow against his rule.

Asked Thursday whether he would seek another term in 2018, Putin said that he doesn't exclude that.