MOSCOW (Reuters) - Around 500 Russian motorised infantry troops are carrying out drills in the mountains of Tajikistan against the backdrop of instability in neighbouring Afghanistan, Russia's defence ministry was quoted as saying on Monday.

       All servicemen involved in the exercise come from the Russian military base in Tajikistan, the Interfax news agency quoted the Central Military District command as saying.

       The current set of drills is the third one carried out by Russia close to the Afghan border this month. Next month, a Russia-led security bloc will hold another exercise in Kyrgyzstan which hosts a Russian military airbase.

       (Reporting by Olzhas Auyezov; Editing by Alison Williams)