"Naturally, we will increase our forces in Crimea because NATO countries have stepped up their activities… in the immediate vicinity of our borders," Alexander Grushko said.
The envoy also said that Russia will act in line with its obligations under international treaties, adding that there was no ban "on deployment of certain types of weapons" in Crimea.
In March, Russian Defense Minister Sergei Shoigu said that Russia had deployed a self-sufficient contingent, consisting of nearly 100 units, in Crimea.
NATO has stepped up its joint military exercises in Eastern Europe as the United States looks to show its commitment to security in the region after what the West said was the "annexation" of Crimea.
The West has also accused Russia of fueling the ongoing armed conflict in eastern Ukraine, a claim denied by the Kremlin.
Moscow has repeatedly expressed its concern over the build-up of NATO forces close to the Russian border as well as the US plans to deploy parts of its anti-missile shield in Europe.