Europe's leaders on Thursday sharply condemned Russia's stand on Ukraine and warned it was readying targeted sanctions within days if Moscow failed to back off and join peace efforts.
Winding up six hours of tough talks to decide a joint response, the European Union's 28 leaders agreed a three-step series of sanctions beginning with the immediate halt of talks on easing visas for Russians as well as discussions over a new economic accord.
A statement demanded that Russia begin negotiations with Ukraine in the next few days, which must "produce results within a limited timeframe," it said.
"In the absence of such results the European Union will decide on additional measures, such as travel bans, asset freezes and the cancellation of the EU-Russia summit" in June.
In a third stage, any steps by Russia "to destabilise the situation in Ukraine would lead to severe and far-reaching consequences for relations... which will include a broad range of economic areas."
"We have got to make sure we get Russia and Ukraine talking to each other," said British Prime Minister David Cameron.
"The Russians will be able to see very clearly the consequences," said Cameron, adding that Britain for its part would look at reviewing its arms sales to Russia.
"I would urge others to do the same," he added. "No area should be off the table"
Ukraine's interim premier Arseniy Yatsenyuk was present at the talks to discuss what EU president Herman Van Rompuy dubbed "perhaps the most serious challenge to security on our continent since the Balkans wars" in the 1990s.
Europe's leaders praised Yatsenyuk and his government for their "measured response" to Moscow's military threat and pledged to unlock a huge aid package of 11 billion euros as rapidly as possible
They also pledged to sign an association accord with Ukraine before the ex-Soviet state holds early elections at the end of May, despite earlier reservations on striking any deals with the interim authorities.
It was the sudden rejection of this pact, years in the making, by ousted president Viktor Yanukovych that triggered pro-EU protests that eventually swept him from power last month.
- Crimea seals EU divisions -
EU nations have been divided on how to respond to Russia's stand on Ukraine, with members from eastern Europe once in the Soviet sphere far tougher than France and Germany, mindful of economic ties with Russia.
When Europe's G8 members, Britain, France, Germany and Italy agreed to suspend preparations for a June summit to be hosted by Putin in Sochi, Berlin and Rome had to be prodded to go along.
"We can't do business as usual," said German Chancellor Angela Merkel on arrival.
"There has to be a return to international law, and that means securing the territorial integrity of every country."
Agreeing with Ukraine's interim Prime Minister, the leaders also dubbed as "illegitimate" a request Thursday by the local parliament in Crimea to become part of Russia.
"We urge the Russian government not to support those who advocate separatism," Yatsenyuk had said.
Pro-Moscow lawmakers in Crimea made the request to Russian President Vladimir Putin and said they would put the question to a referendum on March 16.
Putin has been building up "a new wall of intimidation, of military aggression," Yatsenyuk said, calling on the Russian president instead to pull that wall down and to build a "new relationship".
French President Francois Hollande said the developments in Crimea had created "a climate that justified us beefing up our level of response."
Leaders of the EU's four G8 nations first met alone with Prime Minister Donald Tusk of Poland, who has been a strong proponent of a harsher response.
Alongside Poland is Lithuania, whose head of state Dalia Grybauskaite warned that a "dangerous" Russia is trying to redraw Europe's borders.
"Russia today is dangerous. Russia today is unpredictable."
Warning of a domino effect, Grybauskaite said Russia's muscular approach in Ukraine now posed a direct threat to former Soviet states and others.