The US State Department announced on Wednesday that the Swedish citizen who is subject to sanctions has traveled to St. Petersburg in Russia to be trained by a Russian paramilitary group.
Restrictions are also directed at the Russian ultranationalist extremist group.
The Swede, who was appointed by the USA, has previously been convicted in Sweden for having planned a bombing against a refugee camp.
He was sentenced to one year and ten months in prison for attempted public destruction.
Expelled from Poland
After serving his sentence, he traveled to Poland to contact extremist groups, with the intention of participating in illegal weapons training.
The Polish security service took the man into custody and deported him to Sweden.
"The US government is deeply concerned about the development of racist threats of violence around the world," said US Foreign Ministry spokesman Ned Price.
At the same time, the US Treasury Department froze assets of the designated Russian nationalist extremist movement.