EU leaders have suspended talks on visa-free travel with Russia and threatened asset freezes and economic sanctions if the situation in Ukraine gets worse.

The immediate cost of Russia’s invasion of Ukraine’s Crimea - described by UK Prime Minister David Cameron as “the one thing the Russians want more than anything with the EU” - is no quick prospect of Russian people visiting Europe without visas.

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EU leaders also shelved talks on a new bilateral treaty with Russia, but these had all-but petered out before the current crisis.

They added that unless Russia starts negotiations with Ukraine’s new government “in the next few days” and agrees in “a limited timeframe” to pull back troops, the EU will impose visa bans and asset freezes on Kremlin officials and cancel the next EU-Russia summit.

They also said if Russia “further … destabilise[s] the situation in Ukraine” there will be “far reaching consequences … which will include a broad range of economic areas.”

The red line refers to Russian aggression in other partly Russophone regions of east and south Ukraine.

Britain’s Cameron indicated the trade sanctions could cover Russian access to EU financial centres, such as the City of London, the energy market, and defence contracts.

For her part, German Chancellor Angela Merkel, whose country buys vast amounts of Russian gas and sells tens of billions of euros of German products in Russia, noted she is ready to take "far reaching economic measures.”

French leader Francois Hollande, who is due to deliver two warships to Russia, said “we respect all contracts that we have signed,” but added “we have to look at all domains … we have to forcefully evoke even this hypothesis [that the ships will not be sent].”

On the Ukrainian side, EU leaders agreed to sign the “political” chapters of an EU-Ukraine treaty before Ukrainian elections in May and to unilaterally lower tariffs on Ukrainian imports.

They also backed a European Commission proposal to pay Ukraine €11 billion in loans and grants in the next seven years in return for an ethnically “inclusive” government and austerity measures.

With the Ukraine crisis originating in its former regime’s refusal to sign the EU accession treaty last year due, in part, to Russian pressure, the commission chief, Jose Manuel Barroso, said the early signature “will seal the association between Ukraine and the EU, as was the wish of the Ukrainian people.”

The EU summit accord was not plain sailing.

Polish Prime Minister Donald Tusk told press that when the meeting began “it looked like it would not be so simple” to get agreement on his proposal on the early EU treaty signature.

France's Hollande noted the association treaty has nothing to do with EU enlargement. “For those of you [in the press] who are not specialists, ‘association’ does not mean ‘integration’ and it does not mean ‘accession’,” he said.

He added that any Russia trade sanctions will require a “new decision” by the EU, creating the opportunity for national vetoes down the line.

With the US earlier in the day already authorising a visa ban and asset freeze on Russian officials, the EU side rejected suggestions that its response is weaker.

Van Rompuy noted the US executive order was “very general” and will be fleshed out later, while EU institutions are already drafting legal instruments for similar measures so that “this step can be taken much earlier ... than people think.”

Barroso said the EU-Ukrainian association pact “is something that we can offer that some of our international partners cannot,” while Merkel added that America’s decision is part of a “co-ordinated approach between the US and Europe.”

For its part, Nato, the West’s defence alliance, the same day also took action.

The US said it is sending an extra six F-15 fighter jets to patrol Nato airspace in the Baltic region and 12 F-16s for a training exercise in Poland.

Directly after attending the EU meeting, Ukrainian PM Arseniy Yatsenyuk spoke with Nato chief Anders Fogh Rasmussen, who promised to “step up our engagement with Ukraine’s political and military leadership, as we are doing just now.”

He also said he will “strengthen our efforts to build the capacity of the Ukrainian military, including with more joint training and exercises, and we will do more to include Ukraine in our cutting-edge multinational projects to develop capabilities.”

But in the meantime, Russia and pro-Russian groups in Crimea created their own new facts.

The devolved Crimean parliament decreed the territory should join Russia and called a referendum on the question in 10 days’ time - a move the EU and the US dubbed “illegal.”

Pro-Russian paramilitaries scuttled a ship to block Ukrainian vessels in Lake Donuzlav and made Crimea a no-go area for international monitors by refusing access to the Vienna-based multilateral club, the OSCE.

Ukrainian civil society activists also reported that Russian nationals continued to come by bus from Russia to eastern Ukrainian cities, such as Donetsk and Kharkiv, to join pro-Russia protests, in which crowds hung Russian flags on municipal buildings in recent days.