Kremlin spokesperson Dmitry Peskov said that if NATO takes such a step, Russia will take additional steps.
In eastern Ukraine, scattered, low-level clashes continue between Ukrainian troops and Russian-backed separatists.
US forces in Europe are now on high alert, citing increased Russian aggression in the region.
Russia has aggravated efforts to ease tensions in eastern Ukraine, and NATO ambassadors met on Thursday to discuss the situation, a NATO official told the Reuters news agency.
He said the Allies expressed concern over the recent major military operations in Ukraine and neighboring Russia.
Ukrainian President Volodymyr Zelensky agreed with the criticism, saying that military exercises and possible provocations at the border are traditional Russian games.
Peshkov, meanwhile, accused Ukrainian forces of instigating the front line in eastern Ukraine, where the fragile ceasefire was violated every day.
Four Ukrainian soldiers were killed in the separatist bombardment near a village in the Donetsk region on March 26, in the deadliest fire in recent months. Since then, only low-level events have occurred.
Russia conducted a military exercise on the Black Sea Peninsula in Crimea last month, including from Ukraine in March 2014.
Rebels in the Donbas region of eastern Ukraine also rely on Russian aid. Western governments say Russia deployed regular troops there, as well as heavy units. This was denied by the Kremlin, who said Russian volunteers were helping the rebels who occupied Donetsk and Luhansk lands in April 2014.
The video of Russian tanks, cannons and armored vehicles that recently entered the Ukrainian border has not been verified on Twitter.
General Ruslan Khomchak, commander in chief of the Ukrainian army, said Russia deployed 26 battalions of 20,000-25,000 troops in Crimea near the eastern border of Ukraine. Russian officials did not confirm this, nor did they give specific figures.
According to General Khomchak, Russia’s rebel troops in eastern Ukraine have about 3,000 officers and military instructors.
Kremlin spokesperson Peskov said the Russian Federation withdrew its armed forces from its territory due to its limitations. He added that he should not worry anyone and that he did not pose a threat to anyone.
The Russian army confirmed this year that the air strike brigade (about 4,000 soldiers) was resettled from Volgograd in southern Russia to Crimea.
Russia has significantly improved its military presence in Crimea, including the Sevadaspole main naval base, since 2014.