Russian President Vladimir Putin on Tuesday slammed the United States and its European allies for having "ignored" key security concerns raised by Moscow amid the ongoing standoff over Ukraine but signaled his intention to continue talks.

Russia has amassed around 100,000 troops on the border of Ukraine, triggering fears of a further incursion into its neighbor since 2014. While the West has been calling for a de-escalation, Moscow has demanded security guarantees, such as precluding NATO's expansion to Ukraine.

"It is already clear...that the fundamental Russian concerns were ignored," Putin said at a news conference with Hungarian Prime Minister Viktor Orban, according to Russian media.

He also insisted on a halt to NATO's eastward expansion, saying Russia would have to engage in "war" with the North Atlantic Treaty Organization in the event that Ukraine is admitted to the alliance and seeks to recapture Crimea, which Russia annexed in 2014.

While maintaining that NATO's door remains open to any country, the United States has suggested room for discussions with Russia on setting reciprocal limits on military exercises in Europe and the placement of offensive weapons.

In a phone call with Russian Foreign Minister Sergey Lavrov on Tuesday, U.S. Secretary of State Antony Blinken called for an "immediate" Russian de-escalation and the withdrawal of troops from Ukraine's borders, according to the U.S. government.

He also reiterated a warning that further aggression against Ukraine would be met with "swift and severe consequences," including economic and financial sanctions, and urged Russia to pursue a diplomatic path, the U.S. government said.