Moscow on Friday warned that the presence of foreign military personnel could destabilize the situation in Ukraine, following deployment of 300 U.S. trainers there this week.
"The participation of instructors and experts from third countries on Ukrainian territory ... of course, does not help to resolve the conflict," President Vladimir Putin's spokesman Dmitry Peskov said, Russian news agencies reported.
"On the contrary, it can seriously destabilize the situation," he said.
About 300 U.S. paratroopers arrived in western Ukraine this week to train three battalions of the National Guard, part of Kiev's forces fighting the pro-Russian insurgency in the east, over the next six months.
The conflict in Ukraine has raged for over a year, killing more than 6,000 people in eastern Ukraine's Donetsk and Lugansk regions. Western countries accuse Moscow of supporting the separatists but Putin says he has no soldiers in Ukraine.