* Obama, Putin still far apart on Ukraine
* Obama has ordered sanctions against Russia
* Putin says he cannot ignore Russian speakers in Ukraine
* Russian parliament leaders say Crimea entitled to choose
President Vladimir Putin rebuffed a warning from U.S. President Barack Obama over Moscow's military intervention in Crimea, saying on Friday that Russia could not ignore calls for help from Russian speakers in Ukraine.
After an hour-long telephone call, Putin said in a statement that Moscow and Washington were still far apart on the situation in the former Soviet republic, where he said the new authorities had taken "absolutely illegitimate decisions on the eastern, southeastern and Crimea regions.
"Russia cannot ignore calls for help and it acts accordingly, in full compliance with international law," Putin said.
The most serious east-west confrontation since the end of the Cold War - resulting from the overthrow last month of President Viktor Yanukovich after violent protests in Kiev - escalated on Thursday when Crimea's parliament, dominated by ethnic Russians, voted to join Russia. The region's government set a referendum for March 16 - in just nine days' time.
European Union leaders and Obama denounced the referendum as illegitimate, saying it would violate Ukraine's constitution.
The head of Russia's upper house of parliament said after meeting visiting Crimean lawmakers on Friday that Crimea had a right to self-determination, and ruled out any risk of war between "the two brotherly nations".
Before calling Putin, Obama announced the first sanctions against Russia since the start of the crisis, ordering visa bans and asset freezes against so far unidentified persons deemed responsible for threatening Ukraine's sovereignty.
Japan endorsed the Western position that the actions of Russia, whose forces have seized control of the Crimean peninsula, constitute "a threat to international peace and security", after Obama spoke to Prime Minister Shinzo Abe.
China, often a Russian ally in blocking Western moves in the U.N. Security Council, was more cautious, saying that economic sanctions were not the best way to solve the crisis and avoiding comment on the legality of a Crimean referendum on secession.
The EU, Russia's biggest economic partner and energy customer, adopted a three-stage plan to try to force a negotiated solution but stopped short of immediate sanctions.
Brussels and Washington also rushed to strengthen the new authorities in economically shattered Ukraine, announcing both political and financial assistance.
Promises of billions of dollars in Western aid for the Kiev government, and the perception that Russian troops are not likely to go beyond Crimea into other parts of Ukraine, have helped reverse a rout in the local hryvnia currency.
In the past two days it has traded above 9.0 to the dollar for the first time since the Crimea crisis began last week. Local dealers said emergency currency restrictions imposed last week were also supporting the hryvnia.
In their telephone call, Obama said he urged Putin to accept the terms of a potential diplomatic solution to the dispute over Crimea that would take account of Russia's legitimate interests in the region.
Putin was defiant on Ukraine, where he said the pro-Russian Yanukovich had been ousted in an "anti-constitutional coup". But he underlined what he called "the paramount important of Russian-American relations to ensure stability and security in the world", the Kremlin said.
"These relations should not be sacrificed for individual differences, albeit very important ones, over international problems," Putin said.
He maintained Moscow was not behind the seizure of Crimea, home of Russia's Black Sea Fleet. Russia says the troops without insignia that have surround Ukrainian bases are "local self-defence units". The West has ridiculed this argument.
The 28-nation EU welcomed Ukrainian Prime Minister Arseny Yatseniuk to an emergency summit, even though Kiev is neither a member nor a recognised candidate to join the bloc, and agreed to bring forward the signing of the political parts of an agreement on closer ties before Ukraine's May 25 elections.
Yatseniuk said after returning to Ukraine that no one in the civilised world would recognise the result of the "so-called referendum" in Crimea. He repeated Kiev's willingness to negotiate with Russia and said he had requested a telephone call with Russian Prime Minister Dmitry Medvedev.
The European Commission said Ukraine could receive up to 11 billion euros ($15 billion) in the next couple of years provided it reaches agreement with the International Monetary Fund, which requires painful economic reforms like ending gas subsidies.
Despite Putin's tough words, demonstrators who have remained encamped in Kiev's central Independence Square to defend the revolution that ousted Yanukovich said they did not believe Crimea would be allowed to secede.
Some said they were willing to go to war with Russia, despite the mismatch between the two countries' armed forces.
"We are optimists. Crimea will stand with us and we will fight for it," said Taras Yurkiv, 35, from the eastern city of Lviv. "How we will fight depends on the decisions of our leadership. If necessary, we will go with force. If you want peace, you must prepare for war."
Alexander Zaporozhets, 40, from central Ukraine's Kirovograd region, put his faith in international pressure.
"I don't think the Russians will be allowed to take Crimea from us: you can't behave like that to an independent state. We have the support of the whole world. But I think we are losing time. While the Russians are preparing, we are just talking."
On the ground in Crimea, the situation was calm although 35 unarmed military observers dispatched by the pan-European Organisation for Security and Cooperation in Europe were denied entry into the peninsula on Thursday after landing in the southern Ukrainian port of Odessa.
A U.N. special envoy who travelled to the regional capital Simferopol on Tuesday was surrounded by pro-Russian protesters, some of them armed, and forced to leave on Tuesday. The United Nations said it had sent its assistant secretary-general for human rights, Ivan Simonovic, to Kiev to conduct a preliminary humans rights assessment.
Ukrainian television was switched off in Crimea on Thursday and replaced with Russian state channels.
The streets largely belong to people who support Moscow's rule, some of whom have become increasingly aggressive in the past week, harassing journalists and occasional pro-Kiev protesters.
Part of the Crimea's 2 million population opposes Moscow's rule, including members of the region's ethnic Russian majority. The last time Crimeans were asked, in 1991, they voted narrowly for independence along with the rest of Ukraine.
"This announcement that we are already part of Russia provokes nothing but tears," said Tatyana, 41, an ethnic Russian. "With all these soldiers here, it is like we are living in a zoo. Everyone fully understands this is an occupation."