• Tensions between Ukraine and Russia heightened over the weekend, after the United States warned that an invasion could be "imminent."
• Dutch airline KLM suspended its flights into Ukraine and other companies are considering doing the same.

LONDON — Ukrainians are starting to feel "abandoned," Ukraine's ambassador to the U.K. told CNBC on Monday, as tensions with Russia escalate and many nations urge their citizens to leave the country.

"The problem is that Ukrainians are pushed, you know, to panic," Vadym Prystaiko, Ukraine's ambassador to the U.K., said Monday.

"The airlines are canceling the flights, money has been withdrawn by investors. Ukrainians feel that they've been abandoned," he said in London.

Tensions between Ukraine and Russia heightened over the weekend, after the United States warned that an invasion could be "imminent." Dutch airline KLM suspended its flights into Ukraine and other companies are considering doing the same.

Given that high level of threat, the U.S. decided to pull some of its staff from Kyiv. European diplomatic services are still operating in Kiev, but different European nations have told their citizens to avoid flying into Ukraine and have asked those residing in the country to leave while commercial means are still available.

Prystaiko said he felt "quite bad" about the U.K.'s decision to warn its people to leave Ukraine.

"Because not many people can leave. My family can't leave, my mom can't leave, my family, my brother lives there — and so many friends. We feel, the word abandoned — maybe this a bit [of a] harsh word, but that's how Ukrainians believe that they've been treated as of now," he said.

"We just wanted to remind everybody ... we don't want this war," he added.

Despite ambitions to join NATO and the European Union, Kyiv is currently not a member of either of these organizations. Therefore, it's more difficult to receive military assistance in the case of a Russian invasion.

In fact, the U.S. and other Western countries have already said they would not be sending troops to Ukraine to fight Russia.

"[We are] not a family of anybody, who would come to help us and support," the ambassador noted, adding that as a result, "we can't expect ... somebody will come to save us."

Earlier on Monday, Prystaiko rowed back on comments from Sunday where he said Ukraine could be flexible" on its ambition to join NATO — a key demand from the Kremlin. Prystaiko confirmed to CNBC that this is still his country's ambition.

For now, while that membership is not available, Ukraine is seeking bilateral agreements to have more support in case of further Russian aggression. "We're flexible enough to look for other arrangements like bilateral [ones]," he said.