Britain's ambassador to Ukraine left the country on Monday, Foreign Secretary Liz Truss told parliament.
"Our ambassador has left Ukraine because of the serious security situation," Truss told the Foreign Affairs Committee, referring to the 12-day-old war.
She added that all UK diplomatic missions in Ukraine are now closed.
Truss said the West had taken its "eye off the ball" in the post-Cold War era and enabled Russian high-tech warfare through its dependence on Russian energy.
She said the Russian war had "shattered the security architecture of Europe," adding that countries "need to rethink their economic dependence" on Russian oil, gas, and coal.
"Defense budgets were cut, there was too much entering into trade and economic relationships without understanding the underlying strategic dependency that would lead to," she said.
"That's particularly true of hydrocarbons, which are of course a major part of the Russian economy, but it's also true of technology exports."
Since Russia began its war against Ukraine on Feb. 24, it has drawn international condemnation, led to financial sanctions on Moscow, and spurred an exodus of global companies from Russia.
At least 406 civilians have been killed and 801 others injured in Ukraine since the beginning of the war, according to UN figures.
More than 1.7 million people have also fled to neighboring countries, the UN Refugee Agency said.
