The Secretary General expressed concerns about Russian "statements about possible future stationing of nuclear weapons and delivery systems in Crimea."
He announced this after a session of the NATO-Ukraine Commission in Antalya, Turkey, on Wednesday.
He also added that NATO is "concerned by Russia's efforts to further build up its presence in the Black Sea region," warning that "this could have further implications on regional stability."
"Russia's annexation of Crimea is illegal and illegitimate; we do not and we will not recognize it," he emphasized.
As UNIAN reported earlier, Director of the Russian Foreign Ministry's department of non-proliferation and arms control Mikhail Ulyanov said that Russia might deploy nuclear weapons in the annexed Crimea.
In 1994, Ukraine decided to scrap its nuclear weapons.
After the session, the Foreign Ministers of the NATO-Ukraine Commission issued an official statement, condemning Russia's ongoing and wide-ranging military build-up in Crimea and reaffirming their strong support for the settlement of the conflict in eastern Ukraine by diplomatic means and dialogue.