Kiev, Ukraine (CNN) -- [Breaking news alert, 1:37 p.m. ET]
-- U.S. Secretary of State John Kerry told reporters Thursday that he spoke with Russian Foreign Minister Sergey Lavrov, and the two have agreed to continue talking "over the course of the next hours, the next days'' to try to find a political solution to end the crisis in Ukraine.
"As you have heard me say all week, the choices that Russia has made escalated this situation, and we believe Russia has the opportunity now ... to de-escalate," he said.
-- President Barack Obama said on Thursday that a proposed referendum for Crimea to join Russia would violate the Ukrainian constitution and international law.
"Any discussion about the future of Ukraine must include ... the government of Ukraine," he said.
[Breaking news alert, 1:14 p.m. ET]
-- Obama said if Russia continues "this violation of international law" in Ukraine, "the resolve of the United States and our allies and the international community will remain firm."
-- The President also called for Congress to support assistance for the Ukrainian government from both the United States and the International Monetary Fund.
-- Interpol said it is reviewing a "red notice" request by Ukrainian authorities for the arrest of ousted Ukrainian President Viktor Yanukovych on charges including abuse of power and murder. A red notice is not an international arrest warrant, but many Interpol member countries consider the alert to be a valid request for provisional arrest, the agency said. Interpol cannot demand that any member country arrest the subject of a red notice.
[Breaking news alert, 1:05 p.m. ET]
-- President Barack Obama will make a previously unscheduled statement on the Ukraine crisis at 1:05 p.m. ET, the White House said Thursday.
-- The European Council said Thursday it will suspend bilateral talks with Russia on visa matters because of the Ukraine crisis.
It also threatened travel bans, asset freezes and cancellation of the EU-Russia summit if there is no timely diplomatic progress. It also said there would be "severe and far-reaching" economic consequences if Russia further destabilizes the situation in Ukraine.
-- European Council President Herman Van Rompuy said European Union leaders meeting in Brussels condemned "Russia's unprovoked violation of Ukrainian sovereignty and territorial integrity," called the referendum for Crimea's future unconstitutional, and urged a solution to the Ukraine crisis "in full respect of international law."
"The situation must de-escalate and failure by Russia to do so will have serious consequences on our bilateral relationship," he said.
-- German Chancellor Angela Merkel said Thursday the European Union wants to do everything it can to settle the Ukraine crisis diplomatically, but said that if there's no "diplomatic possibility," steps such as asset freezing and visa limitations would be options.
[Original story published at 12:29 p.m. ET]
Ukraine PM Yatsenyuk: Crimea 'was, is and will be an integral part of Ukraine'
We're leaving. No, you're not.
That's where the crisis in Ukraine stood Thursday after lawmakers in Crimea voted in favor of leaving the country for Russia and putting it to a regional vote in 10 days.
It's an act that drew widespread condemnation, with Ukrainian interim Prime Minister Arseniy Yatsenyuk calling the effort to hold such a referendum "an illegitimate decision."
"Crimea was, is and will be an integral part of Ukraine," he said.
It's not clear how easily the region could split off from Ukraine, if the referendum endorses the move.
The developments came as Yatsenyuk joined in emergency talks in Brussels, Belgium, called by leaders of the European Union who support the Kiev government and want to de-escalate the crisis.
The EU and the United States announced plans to freeze the assets of Viktor Yanukovych, who was ousted as Ukraine's President after he turned his back on a trade deal with the EU in favor of one with Russia. That prompted months of protests that culminated in February with bloody street clashes that left dozens dead and Yanukovych ousted.
Moscow has denounced the events that led to Yanukovych's ouster as an illegitimate coup and has refused to recognize the new Ukrainian authorities, putting the two countries on a collision course over control of the Crimean region, a peninsula on the Black Sea.
Russian President Vladimir Putin has insisted he has the right to use military forces in Ukraine if necessary to protect ethnic Russians under threat in Crimea, an allegation that Ukrainian officials say he made up as an excuse to take control of the region.
In a sign of perhaps just how serious the confrontation between Russia and the West has become, U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov met face-to-face to try to calm the dispute.
But there were signs the divide between the two sides was widening.
A draft statement circulated among EU nations said that Russia's failure to "de-escalate" the crisis would have "serious consequences" on European-Russian relations. The statement, which was distributed late Wednesday, does not spell out what consequences Russia would face.
At the EU talks, Yatsenyuk said the proposed referendum "has no legal grounds at all."
"That's why we argue that the Russian government should not support those who claim separatism in Ukraine."
He urged Russia to pull back its forces from Crimea and engage diplomatically. "If they are ready to talk, we are -- and we made it very clear," he said.
Putin has denied claims by Ukrainian officials and Western diplomats that Russia has sent thousands of troops into the region in recent days. Russia says the heavily armed troops, who are in uniforms without insignia and who have reportedly encircled Ukrainian bases, are local "self-defense" forces.
As the standoff in Crimea continued, Ukrainian authorities announced the arrest Thursday of a leader of a pro-Russian movement in the eastern city of Donetsk. Authorities said he is a Ukrainian national named Pavlo Gubarev, a self-proclaimed governor of Donetsk.
U.S. visa ban imposed
Amid the rapidly shifting diplomatic sands, European Union leaders are discussing possible economic and diplomatic sanctions against Russia, which could include asset freezes or visa moves.
Kerry spoke at some length with Lavrov in Rome on Thursday, on the sidelines of a meeting on Libya.
Kerry urged Russia to begin talks with Ukraine and allow international monitors into the Crimean region to see first-hand how the crisis is playing out on the ground, a senior U.S. official told reporters after the meeting Rome.
The Organization for Security and Co-operation in Europe said its team of observers, invited into the country by the government in Kiev, had been turned back as they sought to enter Crimea.
Lavrov has criticized moves by the OSCE and NATO, which has suspended some joint undertakings with Russia, saying their actions "are not helping to create an atmosphere of dialogue and constructive cooperation."
The U.S. State Department imposed a visa ban on Russian and Ukrainian officials and others that is says are responsible for, or complicit in, threatening the sovereignty and territorial integrity of Ukraine.
President Barack Obama also signed an executive order laying the groundwork to impose sanctions against individuals and entities responsible for the crisis.
The United States also is adding six F-15 fighter planes to the four currently on a NATO mission in the Baltics, the Pentagon announced Wednesday, and the guided-missile destroyer USS Truxtun is about to take part in a previously scheduled exercise in the Black Sea.
The impact of EU sanctions, if they were imposed, might be felt by other countries, too. Russian lawmakers are drafting a law that would allow the nation to confiscate assets belonging to U.S. and European companies if sanctions are slapped on Moscow, Russian state media reported Wednesday.
The Russian threat was not specific, but numerous large European and U.S. companies have interests in the region. Russia is also a major supplier of natural gas to Europe.
Martin Schulz, president of the EU Parliament, earlier promised in remarks alongside Yatsenyuk that Europe stood behind the new government in Kiev and a peaceful, democratic future for Ukraine.
"We are behind you and your government, and we support you with all our means," he said.
This includes ensuring that an 11 billion-euro aid package offered Wednesday by the European Union gets to Ukraine as soon as possible to shore up the cash-strapped economy, Schulz said.
Nuclear issue
Justice Minister Pavlo Petrenko told journalists in Kiev that the Crimean parliament's decision is illegal because under the constitution, only national referendums are permitted, a Justice Ministry spokeswoman said.
The parliament in Crimea installed a new, pro-Moscow government late last month -- as armed, pro-Russian men besieged the parliament building -- and does not recognize the authorities in Kiev.
Citizens will be asked on March 16 if they want an autonomous republic of Crimea within Russia; or within Ukraine.
The autonomous region has a 60% ethnic Russian population, having been part of Russia until it was ceded to Ukraine in 1954 by the Soviet Union. But not everyone may be as keen on coming under Moscow's direct influence. A quarter of the peninsula's population is Ukrainian and about 12% Crimean Tatars, a predominantly Muslim group.
Michael Crawford, a former British ambassador in Eastern Europe, cautioned that whatever the result of the vote, it may be meaningless.
"It does not follow that if Crimea votes to join Russia, that anyone will accept it," he said.
"For Russia to start cherry-picking bits of the former Soviet Union, cranking up referenda in Kazakhstan or Latvia or wherever you like, to try to carve off bits, would be against international law, and it would be something Vladimir Putin has said he doesn't want to do."
Yatsenyuk said that if Ukraine is broken up, the world will have trouble ever getting another country to give up its nuclear weapons program.
Why? In 1994, Ukraine agreed to give up its Soviet-era nuclear arsenal in return for guarantees -- signed by the United States, the United Kingdom and Russia -- of its territorial integrity and independence.
What happens now to Ukraine "will have an impact on nuclear nonproliferation programs," Yatsenyuk said.
