More than 1 trillion roubles' ($11 billion) worth of strategic enterprises and assets were transferred to state ownership by Russian courts last year, Prosecutor General Igor Krasnov said on Tuesday.
The assets, according to the prosecutor's office, are critical for developing Russia's economy and strengthening its defence capabilities. President Vladimir Putin has said there is no widespread nationalisation taking place.
"They had been taken out of the ownership of the Russian Federation by illegal, including corrupt, means," Krasnov told Putin in a televised address to a prosecution service conference.
"Moreover, some of their funds were even being directed to finance terrorist activities on the part of Ukraine."
Russia, which sent its armed forces to seize parts of Ukraine in 2022, regularly accuses Kyiv of carrying out "terrorist activities", notably to attract aid and weapons from the West. Kyiv says its actions on Ukrainian and Russian territory are legitimate self-defence.
"Based on the real value of the assets, the amount is more than 1 trillion roubles," Krasnov said.
Prosecutors have been seeking to nationalise assets important to the defence industry that they say were privatised illegally in the 1990s, such as electrometallurgical and ferroalloy plants in Chelyabinsk, the Kommersant daily reported last month.
Putin last year told companies that no one would be prosecuted for simply being in business, provided they complied with Russian legislation.
But on Tuesday he said that seizures were justified when assets had been acquired illegally or were being used to the state's detriment.
"I would like to outline my position here: there is no de-privatisation or nationalisation of the economy, there is and can be no question," Putin said.
Last week, Bank of Russia Governor Elvira Nabiullina expressed concern that retail investors were being forced to give up shares bought on the market.
"If we want to attract resources for development, including using capital market opportunities, then, of course, maintaining trust is super-important," Nabiullina said. ($1 = 92.7560 roubles) REUTERS
