Russia has strengthened its southwestern flank as NATO builds up its military presence near its borders and next-door Ukraine remains unstable, Russian Defence Minister Sergei Shoigu said on Wednesday.

Moscow has deployed more air defence systems in the southwest and has also deployed a "self-sufficient" contingent of troops in Crimea, Shoigu told a meeting at the Defence Ministry broadcast on state television.

"Since 2013 ... we have formed four divisions, nine brigades and 22 regiments," he said. "They include two missile brigades armed with Iskander missile complexes, which has allowed to boost fire power to destroy the potential adversary."

Shoigu said "terrorist" groups were also active in the North Caucasus