Russian President Vladimir Putin has moved to legalise the military's use of foreign volunteers in overseas operations, a new step in the country's increasing engagement in wars abroad.

A decree published on Monday - though still not ratified by Parliament - would allow foreign nationals to serve in what the law calls "counterterrorism and peacekeeping missions," including in Syria, where increasing numbers of Russian service members are currently stationed.

Russian President Vladimir Putin attends a summit of the Ex-Soviet Alliance leaders in Sochi, Russia. Credit:AP

"The timing of the change is quite telling," said Alexey Khlebnikov, an analyst with the Russian International Affairs Council.

"Russia's only military operation abroad is in Syria, and only contractors [volunteers as opposed to conscripts] are serving there. This amendment provides regulation for the foreign nationals who participate in Russia's Syria campaign."