The Kremlin insisted it has no intention to invade Ukraine, saying its posture is purely defensive.
Russia has said it could not de-escalate tensions with the West over Ukraine due to a large concentration of Ukrainian forces near its border.
"Russia cannot take any measures to de-escalate," Kremlin spokesperson Dmitry Peskov told reporters on Wednesday.
"We have seen the messages that more than 120,000 Ukrainian troops have been deployed to the conflict zone. This raises our fears that sentiments in Ukraine in favour of a military solution to the Donbass problem could prevail," Peskov said.
"This is very dangerous adventurism. All this causes us deep concern because this is happening in the immediate vicinity of our borders."
Meanwhile, President Vladimir Putin has said that Moscow would seek Western guarantees that would preclude any further NATO expansion and deployment of its weapons near Russia's borders.
Speaking at a Kremlin ceremony where he received credentials from foreign ambassadors, Putin emphasised Russia will seek “strong, reliable and long-term guarantees of its security.”
Statements from Russia came amid Ukrainian and Western worries about an alleged plan by Moscow to invade Ukraine.
Tensions have been soaring in recent weeks about a Russian troop buildup near Ukraine, which worried Ukrainian and Western officials, who saw it as a possible sign of Moscow's intention to invade its ex-Soviet neighbour.
NATO foreign ministers warned Russia on Tuesday that any attempt to further destabilise Ukraine would be a costly mistake.
The Kremlin has insisted it has no such intention and has accused Ukraine and its Western backers of making the claims to cover up their own allegedly aggressive designs.
The Kremlin also said its posture is purely defensive.