MORE: Ukraine behind killing of Russian chemical weapons general in Moscow blast, sources say The suspect, whose name has not been released, had been recruited by Ukrainian intelligence officers, Russian police said as they announced the arrest.

Igor Kirillov, who was named the head of Russia’s nuclear defense forces in April 2017, was under sanctions from several countries including the U.K. and Canada for his role in Ukraine.

A top Russian general accused of using chemical weapons on the battlefields in Ukraine was killed after a bomb went off in Moscow early Tuesday, Russian investigators said, in an attack swiftly claimed by Kyiv.