• Relations between the Kremlin and its European counterparts hit a low in 2014 when Russia annexed Crimea from Ukraine.
• Republican Senator Mitt Romney told NBC on Sunday that he believed Russian President Vladimir Putin wants to reestablish a "type of Soviet Union."
• Russian President Vladimir Putin has made no bones about the fact that he thinks the breakup of the Soviet Union was a catastrophe for Russia.

BRUSSELS — Russia needs to move forward in the world and stop dreaming about reconstructing the Soviet Union, a prominent Ukrainian diplomat has told CNBC as tensions with Moscow escalate.

"Russia needs to reinvent itself as a modern state and stop clinching to the, let's say, idea of the reconstruction of the Soviet Union," Vsevolod Chentsov, the Ukrainian ambassador to the EU, told CNBC Tuesday.

"It's already gone," he said regarding the Soviet bloc which collapsed in 1991.

Relations between the Kremlin and its European counterparts hit a low in 2014 when Russia annexed Crimea from Ukraine. And it has supported a pro-Russian uprising in the east of the country where low-level fighting between Ukrainian forces and pro-Russian troops has continued ever since.

Now, U.S. officials are warning that Russia could be weighing a potential invasion of the former Soviet republic Ukraine, with the Kremlin moving 100,000 troops close to the border. Geopolitical analysts suggest that Moscow's actions, and any incursion, would be an attempt to boost Russian influence in other parts of the region.

Republican Senator Mitt Romney told NBC on Sunday that he believed Russian President Vladimir Putin wants to reestablish a "type of Soviet Union" and "that can't be allowed to happen."

Russian President Vladimir Putin has made no bones about the fact that he thinks the breakup of the Soviet Union was a catastrophe for Russia, once describing it as the "greatest geopolitical tragedy" of the 20^th century.

Evolution of the EU position

Other experts suggest that the Kremlin is instead trying to destabilize the European Union, the 27-member bloc that it shares several borders with. Chentsov, who works closely with Brussels, said that if this is Putin's plan, then it is not working.

"There is more unity among the member states and more understanding of Russian actions," he told CNBC.

"We [have] witnessed [a] gradual evolution of the EU position towards Ukraine, towards the crisis," he said, mentioning the various statements and visits from European officials to Kyiv.

Germany's Foreign Affairs Minister Annalena Baerbock — who is among the recent flurry of European politicians to visit Ukraine — said in Moscow on Tuesday that there is "no understandable reason" for the Russian military buildup close to Ukraine.

She added that it is "hard" not to see this move as a "threat." Meanwhile, Ukrainian officials have complained about Germany's reluctance on sending defensive weapons to help out Kyiv.

"We would like to have more assistance. Also material assistance from our partners like Germany," Chentsov said, adding that the intention is not to attack Russia, but to be able to protect Ukraine in the event of further military aggression.

When asked if Kyiv recognized that a potential German decision to send weapons to Ukraine could escalate tensions with Russia even further, Chentsov said: "We do not share this logic that it would make the situation worse."

"We hope that the new government in Germany, they ... take a fresh look at the situation," he said.

Speaking on Monday in Kyiv, Germany's Baerbock played down the chances of Berlin changing its mind, reportedly saying the German government will be supporting Ukraine "by other means."

The German position contrasts with a U.K. announcement on Tuesday which stated that it would be supplying Kyiv with defensive arms. British Defense Secretary Ben Wallace said these weapons have a "short range" and do not pose a threat to Russia, Sky News reported.

Blinken to visit Ukraine

Meanwhile, U.S. Secretary of State Antony Blinken spoke with Sergey Lavrov, Russia's foreign affairs minister, Tuesday ahead of his trip to Ukraine and Germany this week.

"The Secretary stressed the importance of continuing a diplomatic path to de-escalate tensions surrounding the deeply troubling Russian military build-up in and near Ukraine," Blinken's office said in a press statement.

These new conversations come just days after failed talks between Russia, the U.S. and other NATO members to resolve the ongoing tensions.

Russia said it is waiting for a written reply from the U.S. and NATO regarding its demand for a de-facto veto on any new members joining the military alliance.

In the meantime, geopolitical tensions continue to build.

On Friday, key Ukrainian government websites were subject to a cyberattack, which Ukraine has already blamed Russia for. In addition, the United States has accused Russia of preparing a pretext so that it could invade Ukraine.

Over the weekend, Sweden also moved troops to its strategically-important island in the Baltic Sea, Gotland.

—CNBC's Holly Ellyatt contributed to this article.