MOSCOW—Russian President Vladimir Putin dismissed his top aide on Friday, a surprise move for a leader who rarely parts with such longtime allies.
Mr. Putin said in televised remarks that Sergei Ivanov, a former intelligence official who has been a key lieutenant of the president for almost two decades, was resigning as his chief of staff and would be succeeded by his deputy.
The president issued an order to relieve Mr. Ivanov of his duties and held a televised meeting with him and his successor. Mr. Putin praised Mr. Ivanov’s work and recalled that Mr. Ivanov had requested not to work as chief of staff for more than four years.
“I respect your desire to move to another line of work,” Mr. Putin said. The president appointed Mr. Ivanov a special representative for transport and environmental issues.
The move is the most high-profile dismissal in years. Mr. Putin has refreshed the top ranks of officials in recent months, from governors to the head of customs. But the president has rarely cast aside anyone as close as Mr. Ivanov, a 63-year-old former defense minister once viewed as a potential successor.
Like Mr. Putin, the urbane, English-speaking Mr. Ivanov studied at Leningrad State University and began his career in the security services in the 1980s. In the late 1990s, he served as Mr. Putin’s deputy in the Federal Security Service and later held several key government posts.
Mr. Ivanov is one of a handful of top officials targeted by U.S. sanctions following Russia’s annexation of Crimea in 2014.
His successor is a little-known 44-year-old, Anton Vayno, who was born in Estonia, then a Soviet republic, to an elite family of Communist Party officials. He worked as head of protocol for the Kremlin and most recently was Mr. Ivanov’s deputy.
Some analysts saw the move as part of a gradual effort to replace close allies with younger, more-malleable yes-men.
“Putin finds it more comfortable to work with people who don’t ask extra questions, who don’t speak to him as an equal,” said Tatiana Stanovaya, an analyst at the Center for Political Technologies, a think tank in Moscow. “Gradually, he is surrounding himself with people who are not connected to him in his former life.”
In the past year, Mr. Putin has removed Russian Railways head Vladimir Yakunin,antinarcotics chief Viktor Ivanov and federal guard-service director Yevgeny Murov.
Meanwhile, tensions between Russia and neighboring Ukraine remained high over Crimea. Ukraine put its forces on combat alert on Thursday as Mr. Putin discussedincreased security measures in Crimea after blaming Ukraine for the deaths of two Russian service members.
Prime Minister Dmitry Medvedev in televised remarks floated the idea of cutting off diplomatic ties with Ukraine, saying that “if there is no other way to influence the situation, the president can probably make such a decision.”
Russian official news agencies reported on Friday that the Ministry of Defense had deployed an advanced S-400 air-defense system to Crimea.