By Dmitry Antonov and Tom Balmforth

MOSCOW (Reuters) - Russia said on Thursday it was clear the United States was not willing to address its main security concerns but kept the door open for further dialogue in their standoff over Ukraine.

Kremlin spokesman Dmitry Peskov said Moscow, which has massed tens of thousands of troops near Ukraine, would not rush to draw conclusions after Washington formally responded to Russian proposals for a redrawing of post-Cold War security arrangements in Europe.

Describing tensions https://www.reuters.com/world/europe/us-urges-de-escalation-over-ukraine-offers-russia-diplomatic-path-2022-01-27 on the continent as reminiscent of the Cold War, Peskov said it would take time for Moscow to review Wednesday's response from Washington. But he said U.S. and NATO statements that Russia's main demands were unacceptable did not leave much room for optimism.

"Based on what our colleagues said yesterday, it's absolutely clear that on the main categories outlined in those draft documents... we cannot say that our thoughts have been taken into account or that a willingness has been shown to take our concerns into account," Peskov said.

"But we won't rush with our assessments," he said.

The nuanced Kremlin reaction made clear that Russia was not rejecting the U.S. and NATO responses out of hand or closing the door to diplomacy.

Russian and Ukrainian dollar bonds, which have been hammered in recent weeks by the crisis, both rose in response to Peskov's comments. Russia's dollar-denominated RTS share index climbed 4%.

Russia denies planning to invade Ukraine but says it wants to enforce "red lines" to protect its own security.

It presented demands in December that NATO halt any further enlargement, bar Ukraine from ever joining and pull back forces and weaponry from eastern European countries that joined the alliance after the Cold War ended.

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The formal U.S. and NATO responses, delivered on Wednesday, were not made public, but both had already rejected Russia's demands while expressing willingness to engage on other issues such as arms control, confidence-building measures and limits on the size and scope of military exercises.

U.S. Secretary of State Antony Blinken said Washington remained committed to upholding NATO's "open-door" policy and NATO said it would not compromise its core principles.

Ukrainian Foreign Minister Dmytro Kuleba, speaking before the Kremlin comments, said Russia was likely to remain on a diplomatic track with Kyiv and the West for at least two weeks.

Kuleba said Kyiv was preparing for all scenarios, but added that Russia's main strategy now was to destabilise Ukraine, including by using hybrid warfare tactics such as cyber attacks and disinformation campaigns.

"We understand that a military operation is something they keep in the pocket, it's not something they put ahead of other options," he said.

Russian Foreign Minister Sergei Lavrov said there was hope of starting serious dialogue with the United States, but only on secondary questions and not on fundamental ones.

"The most important question is our clear position on the unacceptability of NATO's further eastward expansion and the deployment of strike weapons that could threaten Russian territory," Lavrov said in comments published on his ministry's website. He said Putin would decide Russia's next move.

Putin, who has not spoken publicly on the crisis for weeks, is due to travel to China next week for the opening of the Beijing Winter Olympics.

He has warned of an unspecified "military-technical response" - something defence analysts say could relate to missile deployments - if Russia's demands are ignored.

TASS news agency quoted a senior Russian foreign ministry official, Vladimir Ermakov, as saying a nuclear missile crisis between Moscow and Washington was unavoidable without measures to ensure restraint and predictability.

Ermakov said Moscow believed Washington was preparing to deploy short and intermediate range missiles to Europe and the Asia-Pacific region.