Europe's leaders call for dialogue at Ukraine summit

"We have got to make sure we get Russia and Ukraine talking to each other," said British Prime Minister David Cameron on arriving for hastily convened talks, held as Crimea's parliament requested that the Ukrainian Black Sea region become part of Russia.

But echoing statements from the leaders of France, Germany, the Netherlands and others, Cameron said it was key to send a message to Moscow that events in Crimea were "unacceptable and should have consequences."

"Were further action to be taken, that would be even more unacceptable and would require even more consequences," he said.

Russian forces took de facto control of strategically important Crimea, home to Kremlin's Black Sea Fleet, following the ouster on February 22 of Ukraine's pro-Moscow president Viktor Yanukovych.

Lawmakers in the majority Russian-speaking peninsula on Thursday made a request to President Vladimir Putin to join Russia, announcing a referendum on the question on March 16.

Invited to attend the summit in a strong symbolic gesture, Ukraine's interim premier Arseniy Yatsenyuk accused Russia of continued provocation around Ukrainian bases in Crimea.

"This is not only a Ukraine-Russia crisis, it is a crisis in Europe," Yatsenyuk said.

The bloc's 28 leaders met a day after the European Union executive offered Ukraine a huge 11-billion-euro ($15 billion) aid package to support its ailing economy and help pay massive gas bill arrears to Russia.

"Germany will support the package intensively," said Chancellor Angela Merkel as Kiev's transitional authorities awaited fresh pledges of support from other nations in Europe and elsewhere.

"There has to be a return to international law, and that means securing the territorial integrity of every country," Merkel said. "We can't do business as usual" with Russia.

She said leaders would talk about "different kinds of sanctions" should Putin refuse to budge and EU sources said a first phase of punitive measures would likely be diplomatic rather than economic.

Europe's G8 members, Britain, France, Germany and Italy, have along with the US, Japan and Canada, suspended preparations for a June summit to be hosted by Putin in Sochi, though Germany and Italy had to be prodded to agree.

EU nations remain divided on how to respond to Russia's stand on Ukraine, with new EU members from eastern Europe once in the Soviet sphere far tougher than the likes of France and Germany.

Thursday's summit initially was called to discuss sanctions but leaders are now likely to allow more time as events in Crimea unfold.

"If we come to the conclusion in the next 24, 48, 72 hours that the de-escalation is not an option, obviously sanctions will be back on the table," said Dutch Premier Mark Rutte.

Leaders of the four G8 nations first met alone with Prime Minister Donald Tusk of Poland, which has been a strong proponent of a harsher EU response.

Standing alongside Poland is Lithuania, whose head of state warned on arriving for the talks that a "dangerous" Russia is trying to redraw Europe's borders, but that the continent's leaders still did not understand.

"Today it is an open and brutal aggression, that is exactly what is happening and we need to understand it," said President Dalia Grybauskaite. "But today I do not see a prompt reaction."

"This is about rewriting of the borders," she added. "Russia today is dangerous. Russia today is unpredictable."