NATO Secretary-General Jens Stoltenberg warned Wednesday that Russia has still shown no signs of de-escalation on the ground, despite claims of withdrawing troops from near Ukraine.

"We have heard the signs from Moscow about the readiness to continue diplomatic efforts, but so far we have not seen any de-escalation on the ground," Stoltenberg said during a press conference outside NATO headquarters in Brussels. "On the contrary, it appears that Russia continues their military build-up."

NATO continues to monitor the situation "very closely," as it remains unclear whether Russia is pulling back, according to Stoltenberg.

"What we see is that they have increased the number of troops and more troops are on their way," he told reporters. "So, so far, no de-escalation but of course, we hear also the message about diplomacy and we are ready to engage in diplomatic efforts with Russia."

Stoltenberg explained that the Russian military has "always moved forces back and forth."

"So, just that we see movement of forces of battle tanks doesn't confirm a real withdrawal," he said. "It has been a big up and down, back and forth, all the way, but the trend over the last weeks and months has been a steady increase in the Russian capabilities close to Ukraine's borders. So Russia retains the capability of a full-fledged invasion of Ukraine without any warning time."

As of Wednesday morning, there were still approximately 100,000 Russian troops at Ukraine's borders, including in Belarus, according to Stoltenberg, who said he hopes the dialogue with Russia will continue and that the claims of withdrawal are true "because nobody has any interest in confrontation or war in Europe."

"We are at a pivotal moment in the history of Ukraine, Europe and global stability," he added. "We look forward to seeing evidence of the withdrawal of troops on Russia's part, but we need to prepare for any eventuality, with that significant escalation of Russian troops that we have seen over the last weeks and months."

Stoltenberg's comments came ahead of a meeting of the military alliance's defense ministers, including U.S. Secretary of Defense Lloyd Austin, to discuss the current crisis.

The Russian military released more videos on Wednesday morning purportedly showing troops pulling back from Moscow-annexed Crimea.

The footage aired on Russian state media, with one video showing a trainload of armour being carried across the Russian-built bridge that connects the Russian-controlled Crimean Peninsula to Russia's mainland. Another video shows military trucks driving out of Crimea across the bridge, which Russian state media described as support troops leaving "exercises."

However, officials in the West and regional analysts continue to caution that they have not yet seen significant movements of Russian troops pulling back from near Ukraine's borders.

Meanwhile, massive military exercises continue in neighboring Belarus and are not due to finish until Sunday. Belarusian Minister of Foreign Affairs Vladimir Makei said Wednesday that "not a single" Russian soldier will remain in the country once those drills end.

-ABC News' Patrick Reevell

Ukrainian President Volodymyr Zelenskyy wished citizens "a happy day of unity" on Wednesday.

Zelenskyy had said on Monday evening that instead of Feb. 16 being "the day of the attack," he would make it "the day of unity" and declared an impromptu national holiday. ABC News has learned that Russian President Vladimir Putin had told his military forces to be ready to invade Ukraine by Wednesday, but it remains unclear whether he has made a decision to attack the neighboring country.

"We are all united by our wish to live, to live in peace, to live a happy life with our families, parents and children. We have the full right to all of this, because we're at home here, in Ukraine," Zelenskyy said in an address on social media Wednesday morning. "Nobody will love our home as much as we do, and nobody can defend our home as we can. I wish you a happy unity day, my blue-yellow ones, a happy day of unity of Ukraine, in the east and west, in the south and north. It works only together, and when it works, we're strong."

As Russia's defense ministry said Tuesday that some forces would pull back from Ukraine's borders after completing military exercises, sources told ABC News that there are troops moving forward closer to the line, including with medical supplies, and being put into firing positions.

The U.S. believes that Russia now has all the necessary pieces in place, including 150,000 troops in the region, to launch a swift and brutal invasion of Ukraine, the sources added -- the reason why Biden administration officials have now publicly been saying Russia could move "at any time."

ABC News has learned that Russian leader Vladimir Putin had told his military forces to be ready to go by Wednesday, but it is still unclear whether he has made a decision to attack his neighbor.

-ABC News' Conor Finnegan