Russian President Vladimir Putin is to remove his long-standing ally Sergei Shoigu as defence minister, the Kremlin has announced.
The 68-year-old had been in the role since 2012 and will be replaced by Deputy Prime Minister Andrei Belousov, an economist with little military experience.
Mr Shoigu is to be appointed secretary of Russia's Security Council.
The Kremlin said the defence ministry needed to stay "innovative".
Reshuffles in Russia don't happen very often so this is a big moment at the top of Russian politics.
But Vladimir Putin remains the person who ultimately calls the shots. It was his decision to start the war in Ukraine and all the big decisions are taken by him.
The appointment of Mr Belousov as defence minister will come as a surprise to many, given his previous experience.
But analysts suggest President Putin is seeking to align the Russian economy more closely with the war effort.
The decision to put an economist in charge of the Ministry of Defence reflectsthe changing priorities of the Kremlin and the huge amounts of money the Russian authorities are now pouring into the war in Ukraine - and Russia's need to boost efficiency in the armed forces.
Kremlin spokesman Dmitry Peskov said the proposed appointment of a civilian showed the role of defence minister called for "innovation".
He said Russia was becoming more like the Soviet Union in the mid-1980s, when a high proportion of GDP went on military spending.
As a result, it was necessary to make sure that military expenditure was better integrated into Russia's overall economy, he added.
"The one who is more open to innovations is the one who will be victorious on the battlefield," he said.
In recent months, there had been rumours that Mr Shoigu's position was growing weaker and that he could lose his job.
In April, one of his deputies - Timur Ivanov - was arrested on corruption charges in a rare move against such a senior official.
And Russia's campaign in Ukraine was meant to last a few weeks at most.Instead, it is now in its third year and has been plagued by military setbacks and big losses in men and materiel.
Although Mr Shoigu will remain in a powerful role as secretary of the Security Council, the move appears to be a demotion for him.
It's not yet clear what will happen to the council's current head, Nikolai Patrushev.
Mr Shoigu has close links with President Putin, often taking him on fishing trips in his native Siberia.
He was given the defence portfolio despite having no military background, which rankled with some of his top brass.
A civil engineer by profession, Mr Shoigu rose to prominence as the head of the emergencies and disaster relief ministry in the 1990s.
In 2023, Mr Shoigu became embroiled in a public feud with Wagner mercenary chief Yevgeny Prigozhin over Russia's conduct of the war.
Prigozhin, who led a short-lived mutiny against Moscow, accused Mr Shoigu of being a "dirtbag" and "elderly clown" in audio messages that went viral.
The mercenary chief died in a plane crash while flying from St Petersburg to Moscow in August 2023. The Kremlin denied it was to blame.
According to unnamed government officials quoted by independent Russian website The Bell, Mr Belousov is seen as a "hard-line defender of the state, who believes that Russia is encircled by enemies".
Like President Putin, he is close to the Russian Orthodox Church. He is said to be a martial arts enthusiast - as is President Putin - who practised karate and the Russian combat sport sambo in his youth.
Before becoming deputy prime minister, he worked for several years as an aide to Mr Putin and was reportedly the only member of the president's economic entourage to support the annexation of Crimea in 2014.
Mr Putin was sworn in as president for a fifth time on Tuesday after winning Russia's recent election with 87% of the vote without facing any credible opponents. He has led Russia since May 2000.
