Russian economist and former economic advisor to President Vladimir Putin Andrei Illarionov has said the cost of maintaining the occupied Crimea and Donbas for Russia stands at US$4 billion annually.

Russia's budget is able to bear such a "burden" forever, the expert said during an online Q&A session with the Ukrainian news outlet Glavred's readers.

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Illarionov said US$4 billion is about 0.3% of Russian GDP, this amount is "absolutely fit," so this amount of money can be spent indefinitely.

"According to official figures, about US$2 billion is spent on Crimea and Sevastopol per year. This is only for civilian purposes, without military ones. Almost the same amount goes for subsidies and additional expenses for occupied Donbas," the expert said.