Russia made no immediate public comment on Amnesty's allegations.
Ukraine estimated in April that more than 28,000 foreigners from 136 countries were fighting in the Russian army, while officials believe Russia deployed some 14,000 North Korean troops to battle Ukraine's 2024 incursion into the Kursk region.
Ukraine also uses foreign fighters, although Amnesty says it cannot conduct inquiries among those held in Russia due to the group's status as a "foreign agent" in the country.
Neither Moscow nor Kyiv discloses the total number of foreign soldiers in their ranks.
"Obviously, there are many individuals who work for the Russian state who know that the people they recruit to go to the front line are victims of trafficking," Callamard said.
"They are complicit in this phenomenon and they should be held accountable," she said.
The average foreigner targeted by recruiters working for Russia is under 40, living in a poorer country and lured by the "promise of a job", she said.
Russia has previously dismissed accusations of coercing foreigners into joining its army.
