NATO chief Jens Stoltenberg on Wednesday said Russia seemed to be building up its forces around Ukraine, despite Moscow announcing the pullback of more troops from the border.

"We have heard the signs from Moscow about readiness to continue diplomatic efforts, but so far, we have not seen any de-escalation on the ground. On the contrary, it appears that Russia continues their military buildup," Stoltenberg said ahead of a meeting of NATO defense ministers. "What we see is that they have increased the number of troops and more troops are on their way."

NATO will continue to monitor the situation and push for diplomacy, he said.

Stoltenberg urged Moscow to prove that it is pulling back troops amid tensions over a military buildup on Ukraine's borders, saying soldiers and tanks often move about.

"It remains to be seen whether there is a Russian withdrawal ... What we see is that they have increased the number of troops, and more troops are on the way," Stoltenberg told reporters at the start of a two-day meeting of NATO defense ministers at the alliance's headquarters in Brussels.

"If they really start to withdraw forces, that's something we will welcome ... They have always moved forces back and forth so just that we see the movement of forces, of battle tanks, doesn't confirm a real withdrawal."

According to Moscow, several units involved in maneuvers on the Black Sea peninsula of Crimea, which Russia illegally annexed from Ukraine in 2014, have now returned to their bases. The state news agency Ria Novosti released a video showing a platoon of tanks and other military vehicles traveling in darkness over the Crimean Bridge that connects the peninsula to mainland Russia.

The Defense Ministry gave little information on the type of forces being withdrawn and how many troops were involved.

In a similar announcement on Tuesday, the ministry said some troops posted to the southern and western military districts – near Ukraine – were being pulled back after the end of drills.

The move raised a glimmer of hope that the crisis along Ukraine's border was easing after weeks of intense diplomacy and threats by the West of punishing sanctions should Russia invade.

But skepticism of Moscow's intentions remains high. Ukraine, the United States, European powers and NATO suggested they could not take Russia at face value and needed independent confirmation.

And other maneuvers that have caused alarm continue, such as Russian military exercises in Belarus, which also borders Ukraine.

"We have not yet verified that Russian military units are returning to their home bases. Indeed, our analysts indicate that they remain very much in a threatening position," U.S. President Joe Biden said on Tuesday.

The U.S. said this week it believed there were 130,000 troops massed near Ukraine and that an attack could take place at any time.

The Kremlin denies any plans to invade Ukraine and says it is within its rights to deploy troops anywhere on its territory.

Furthermore, it counters that in order to defuse the crisis, the U.S. and NATO must meet Moscow's far-reaching security demands, such as an ironclad promise that the Western military alliance will not expand further eastward. That proposal has been repeatedly shot down.

The defense ministers of the 30 NATO countries – including U.S. Defense Secretary Lloyd Austin – will discuss plans for additional deterrence against Russia later on Wednesday in Brussels.

NATO allies have been sending more ships, fighter jets and troops to Eastern Europe and putting other soldiers on standby.

Meanwhile, Ukraine has earmarked Feb. 16 as a "day of unity." President Volodymyr Zelenskyy declared the day earlier this week after reports in U.S. media cited Feb. 16 as a day Russia could launch an attack.