A British Parliamentary committee says the European Union and Britain are guilty of "sleepwalking" into the crisis in Ukraine.
The EU Committee of the House of Lords made the criticism in a report released on February 20 as a cease-fire brokered by Germany and France falters between Ukrainian forces and pro-Russian separatists in the country's east.
The West and Kyiv accuse Russia of arming the rebels and sending soldiers into Ukraine, something Moscow denies.
The committee's report accuses Britain of not being "active or visible" enough in dealing with the situation, blaming cuts in the Foreign Office, which it says meant it had fewer Russian experts and put less emphasis on analysis.
It adds that a similar decline in EU foreign ministries left them ill-equipped to offer an "authoritative response" to the Ukraine crisis.
The document also says the EU's relationship with Russia had long assumed an "optimistic premise" that the country was on the path to becoming more democratic.
The result, the committee said, was a failure to appreciate the depth of Russian hostility to EU plans for a closer relationship with Ukraine.
The EU and Kyiv signed an Association Agreement on closer political and economic ties in 2014 amid the Russian annexation of Ukraine's Crimea Peninsula and a conflict with pro-Russian separatists in the east of the country.
Committee Chairman Lord Tugendhat said, "The lack of robust analytical capacity, in both the U.K. and the EU, effectively led to a catastrophic misreading of the mood in the run-up to the crisis."
The report says neither Britain nor the EU had a strategic response on how to handle Russia for the long term.
It adds that Britain had a particular responsibility to Ukraine because it was one of four signatories to the 1994 Budapest Memorandum guaranteeing Ukraine's territorial integrity.
A Foreign Office spokeswoman rejected the criticism, saying no one could have predicted the scale of the "unjustifiable and illegal" Russian intervention in Ukraine.
"The blame lies squarely with the pro-Russian separatists, backed by the Russian authorities, not with an Association Agreement between the EU and Ukraine, which had been under negotiation for more than seven years before Russia decided to illegally invade and then annex part of its neighbor," the BBC quoted the spokeswoman as saying.
The report comes as European Council President Donald Tusk called British Prime Minister David Cameron to discuss how the EU should respond to the continuing violence in east Ukraine.
A statement quoted Tusk as saying the EU would be "scrutinizing the situation on the ground very closely in the coming days."
It added that both leaders agreed that European member states would need to "review the EU's response accordingly."
"They agreed that the EU should make clear to Russia that the pro-Russian rebels must abide by the cease-fire," the statement added.
This week, British Defense Secretary Michael Fallon said Russia posed a "real and present danger" to Estonia, Lithuania, and Latvia and NATO was preparing for possible attacks against the Baltic states.
And Foreign Secretary Philip Hammond said on February 19, "There is no doubt that we're seeing a more aggressive behavior by the Russians, by [Russian President Vladimir] Putin, both in Ukraine and elsewhere, testing NATO's defenses."
"We are ready for that, we will remain resolute and united in the face of any provocation," he added.
He also said his country remained opposed to arming Ukraine, but noted the question was "one for individual national governments."
With reporting by AFP and the BBC