Patrushev, the Russian Security Council secretary, told RIA Novosti, Moscow has "grave doubts" Russia will be more secure due to NATO expansion).
"NATO represents a rather serious threat to us," he said.
NATO's post-Cold War expansion has included the majority of Moscow's former Eastern European allies and some former Soviet republics -- a situation the Kremlin regards as dangerous.
The news and information agency said Patrushev blasted NATO for continuing its bid to enlarge, citing its encouragement of efforts by Georgia and Ukraine to join the alliance.
The security chief also reportedly laid the blame for Georgia's military efforts to reel in the breakaway republics of South Ossetia and Abkhazia at NATO's doorsteps, saying the Western alliance armed and encouraged Tblisi.
RIA Novosti said Patrushev asserted NATO countries continue to supply Georgia with weapons.