Political scientist Alexander Dugin is an extreme Russian nationalist closely associated with the Ukraine conflict.
The US said it was cutting business ties and freezing the assets of him and others who had destabilised the situation in the east of the country.
A ceasefire, albeit not fully observed, has been in place for a month.
Russia said it found the new wave of sanctions "difficult to understand".
"We categorically do not see any link between what has recently been happening in south-eastern Ukraine and these sorts of actions," Deputy Foreign Minister Sergei Ryabkov told the news agency Interfax.
President Barack Obama and European leaders have used sanctions as its main form of retaliation for Russia's annexation of Crimea and backing of separatists groups in eastern Ukraine.
"If Russia continues to support destabilising activity in Ukraine and violate the Minsk agreements and implementation plan, the already substantial costs it faces will continue to rise," said Adam Szubin of the US treasury department.
Among those targeted for sanctions is former prime minister Mykola Azarov and two other top Ukrainian officials in former President Viktor Yanukovych's inner circle, for "misappropriation of Ukrainian state assets".
Also included are five officials in the self-proclaimed Luhansk and Donetsk's people's republics and the leaders of Eurasian Youth Union, including Alexander Dugin.
Mr Dugin, a prominent Russian ultra-nationalist philosopher, has called on President Vladimir Putin to intervene militarily in eastern Ukraine "to save Russia's moral authority".
The US says the Eurasian Youth Union has "recruited individuals with military and combat experience to fight on behalf of the self-proclaimed DPR and has stated that it has a covert presence in Ukraine".
A Russian bank operating in Crimea, now the largest banking network in the region, has also seen its assets blocked by the US.
In a separate development, the US is preparing to send more non-lethal aid to Ukraine, including unarmed drones, an unnamed official told US media on Wednesday.

The Sky Blues had the better of a tight contest and came closest to finding a winner when a 25-yard strike by Jacob Murphy hit the post after the break.
Gillingham had started brightly with Dominic Samuel wasting a good opening when he slipped at the vital moment.
Gael Bigirimana also went close with a curling shot for City, who dropped to 11th, nine points off the play-offs.
The Gills are now 10 points off top spot following Wigan's win over Shrewsbury, but they have a game in hand on the Latics and second-placed Burton.
Covnetry City boss Tony Mowbray told BBC Coventry & Warwickshire:
"I think late on we should have won that. It was alright, although for most of it was a pretty poor football match.
"We had a gameplan and it nearly paid off.  We nearly came away with a 1-0 victory but it wasn't to be."
The United States has imposed sanctions on 14 Ukrainian separatists and Russians, including an idealogue who has heavily influenced the Kremlin.
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Mid-table Coventry City earned a point from a drab match as Gillingham missed the chance to go third in League One.