The United States on Tuesday warned Moscow of damaging sanctions, including high-tech export curbs, as Russian combat troops massing around Ukraine launched new exercises.
"We are prepared to implement sanctions with massive consequences" that go far beyond previous measures implemented in 2014 after Russia invaded Ukraine's Crimea region, a senior U.S. official said.
"The gradualism of the past is out," the official told reporters, speaking on condition of anonymity.
British Prime Minister Boris Johnson echoed the threat, saying sanctions would be "heavier than anything we've ever done before."
New measures would include restrictions on exports of high-tech U.S. equipment in the artificial intelligence, quantum computing and aerospace sectors, the U.S. official said.
"What we're talking about are sophisticated technologies that we design and produce" and cutting them off would hit President Vladimir Putin's "strategic ambitions to industrialize his economy quite hard," the official said.
In a bid to break the growing tension, French President Emmanuel Macron said he would talk by telephone with Putin on Friday, seeking "clarification" on Moscow's intentions.
New Russian military exercises
A day after Washington said it was putting 8,500 U.S. troops on alert for possible deployment to bolster NATO forces in Europe, the Russian military announced it was conducting new drills involving 6,000 troops near Ukraine and within the Crimea region.
The drills included firing exercises with fighter jets, bombers, anti-aircraft systems and ships from the Black Sea and Caspian fleets, the defense ministry said.
According to Western officials, the Kremlin has already deployed more than 100,000 troops on Ukraine's borders, with reinforcements arriving from all over Russia.
"We continue to watch the accumulation of significant combat power," Pentagon spokesman John Kirby said.
According to White House Press Secretary Jen Psaki, the U.S. assessment is that the risk of invasion "remains imminent."
Canada announced it was following Britain and the United States in pulling families of its diplomats out of Ukraine.
The United States and its EU allies accuse Russia of seeking to upend European stability by threatening the invasion of Ukraine, a former Soviet republic striving to join NATO and other Western institutions.
Moscow denies plans to invade the country, where in addition to seizing Crimea it backs separatist forces controlling a swath of eastern Ukraine.
Russia instead blames the West for the tension and has put forward a list of demands, including a guarantee that Ukraine never join NATO and that NATO forces already in the former Soviet bloc pull back.
Addressing European concerns that Russia could curb energy exports to heavily dependent Europe in retaliation against sanctions, the senior U.S. official said Russia would also be hurting itself.
"If Russia decides to weaponize its supply of natural gas or crude oil, it wouldn't be without consequences to the Russian economy," a senior U.S. official told reporters.
Although the European Union sources about 40 percent of its supply from Russia, Moscow also relies heavily on sales of energy for its national budget, meaning "it's an interdependency," the official said.
The United States and its European allies are scouring global markets for alternative energy sources to mitigate the fallout from any conflict, as Europe already finds itself struggling with soaring mid-winter energy prices.
Negotiations in European cities this month have failed to ease tensions, though US Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov agreed at a meeting in Geneva on Friday to keep talking.
In addition to the Macron-Putin talks later, the French government said Russian and Ukrainian officials would meet, along with French and German counterparts, in Paris on Wednesday.
Washington has promised to provide written answers to Moscow's demands this week, while already making clear that it rejects giving Russia a veto on Ukraine's aspirations to join NATO.
But the crisis has laid bare divisions in the West.
The new government in EU economic powerhouse Germany, in particular, has faced criticism from Kyiv over its refusal to send defensive weapons to Ukraine, as well as hesitating over one of the harshest economic sanctions under discussion – cutting Moscow from the global SWIFT payments system.
Ukraine's military is heavily outgunned by Russia and no Western country is considering deploying troops to help repel any attack by Moscow.
However, the United States has stepped up deliveries of weapons, with Blinken on a visit to Kyiv last week confirming another $200 million in aid. A shipment arrived on Saturday and another batch was due Tuesday.
At a ceremony for the latest shipment arriving in Kyiv, U.S. charge d'affaires Kristina Kvien said "our preference is diplomacy."
But in case of attack by Russia, "the Kremlin will face fierce resistance, the losses to Russia will be heavy."
"If President Putin decides to make this reckless choice, we will provide additional defensive material to the Ukrainians above and beyond what we’ve already sent," she said.