Russia has so far conscripted and sent around 10,000 naturalized men to fight in its more than two-year-long war against Ukraine, a senior official said on Thursday.
"We have already caught more than 30,000 [immigrants] who received citizenship and did not want to register for military service, and sent about 10,000 of them to the special military operation zone," the head of the Russian Investigative Committee, Alexander Bastrykin, said at the St Petersburg Lawyers' Forum.
Bastrykin was a fellow student of President Vladimir Putin and is considered a close confidant of the Kremlin chief.
The conscripted men are primarily responsible for digging trenches and building fortifications, according to Bastrykin. "You need really strong hands for that," he said.
In recent months, the security forces repeatedly carried out raids on businesses with migrant labourers - primarily from the post-Soviet states in Central Asia.
Those who already received Russian passports are then often forcibly recruited, Russian media reported. Others are promised an easier naturalization process if they are sent to the front.
According to Putin, a total of 700,000 Russian soldiers are currently on the front line in Ukraine. Some of these were recruited in a partial mobilization in autumn 2022.
As the measure was unpopular, the Kremlin wants to avoid further waves of mobilization and find other ways to replenish heavy battlefield losses.