Ukraine's Defense Minister Oleksii Reznikov told parliament on Friday that Russia has massed over 94,000 troops near the border.
Citing intelligence reports, Reznikov also expressed concern that preparations could be underway for some form of escalation as soon as January.
"Our intelligence service analyzes all scenarios, including the worst ones. It notes that a probability of a large-scale escalation on the part of Russia exists. The most probable time when [Russia] will be ready for the escalation is the end of January," Reznikov said.
Ukraine interested in diplomatic resolution
The defense chief said that while Kyiv would not provoke the situation, it was prepared to respond should there be an attack from Russia. He also said, "Ukraine is most interested in a political and diplomatic resolution."
Reznikov also said Ukraine was forging ahead with the construction of two naval bases as part of a defense deal with Britain.
Both of these bases would be near the Crimean Peninsula, which was annexed by Russia in 2014.
Ukraine has also been pushing its allies to prepare sanctions against Moscow in a bid to avert any potential attack.
Meanwhile, Moscow has denied any plan to invade Ukraine and accused Kyiv of raising its own forces to attack territory held by pro-Russian separatists in eastern Ukraine.
Speaking on state television, Russian lawmaker Konstantin Kosachev reemphasized that there was no plan to attack.
"We don't have any plans to attack Ukraine. We don't have any heightened military activity near Ukraine's borders. There is no preparation underway for an offensive," Kosachev told TV channel Russia-24.
US-Russia talks not yet finalized
Efforts are underway to arrange a video call between US President Joe Biden and Russian President Vladimir Putin.
The Kremlin said on Friday that it had a tentative date for a video meeting but was waiting for Washington to agree on the date and time.
Kremlin Advisor Yuri Ushakov said Russia was looking for assurances that NATO would stop expanding east.
"Given the tense situation, there is now an urgent need to provide us with appropriate guarantees. It simply cannot go on like this," Ushakov told reporters at a briefing.
Later on Friday, White House Press Secretary Jen Psaki declined to specify whether military intervention was part of Biden's plan to support Ukraine. "Security assistance," she said, was "under consideration."
Psaki said strict economic sanctions were definitely on the table if Russia invaded.
On Thursday, US Secretary of State Antony Blinken warned Russian Foreign Minister Sergey Lavrov that there would be "serious consequences" for any Russian aggression in Ukraine.
Meeting on the sidelines of an Organization for Security and Co-operation in Europe foreign ministers meeting in Stockholm, Blinken said he told his Russian counterpart that "the best way to avert crisis is through diplomacy."
Lavrov accused NATO of failing in its peacekeeping commitments by "refusing to constructively examine our proposals to de-escalate tensions and avoid dangerous situations."
kb/sms (AP, Reuters)