At some point the West's warnings will have to become deeds, part of the problem is they don't know which Putin they're dealing with.
Rugged Russian President Vladmir Putin visited a centre for endangered Persian leopards at Sochi National Park.
These are difficult days for Ukraine, a country edging toward its second revolution in a decade.
After President Putin signed a decree recognising Crimea as a sovereign state William Hague has said the referendum was not legitimate and its outcome was not legal.
The Foreign Secretary said:
We are witnessing a clear attempt to pave the way for the annexation of part of the sovereign territory of an independent European state, through military force and an illegal and illegitimate referendum.
The UK calls again on Russia to enter into dialogue with Ukraine and with the international community to resolve this crisis through diplomacy and in accordance with international law, not to exacerbate it further through unilateral and provocative actions.
Continuing to ignore those calls will bring serious consequences for Russia. We will urgently consider our response to this latest escalation with our allies and partners, including at the European Council this week.
Vladimir Putin has told President Obama in a telephone conversation that today's referendum in Crimea is compliant with international law, a Kremlin spokesman has said.
The Russian President also told his American counterpart that observers from the Organisation for Security and Co-operation in Europe (OSCE) should be deployed all over the Ukraine.
The two men also agreed that, in spite of their countries' differences of opinion, they should work together to stabilise the situation.
Vladimir Putin has told Angela Merkel an upcoming referendum in Crimea is in accordance with international law.
In a phone call between the two leaders, Putin said the actions of the Crimean parliament were aimed at protecting the legitimate interests of the population in the peninsula.
A statement from the Kremlin added that, while Putin and Merkel differed in their view on the situation in Ukraine, they were agreed that a de-escalation of tensions should be achieved as soon as possible.
Russian President Vladimir Putin's efforts to de-escalate the crisis in Ukraine have been met with no understanding, his spokesman said.
Dmitry Peskov said: "Regardless of all the efforts of our president, his readiness to explain Russia's position practically on a daily basis, we still hit a wall of no understanding.
"It is rather sad and what is worse is that it is very bad from the point of view of possible repercussions."
President Barack Obama has urged Russian President Vladimir Putin to accept the terms of a potential diplomatic solution to the Ukraine crisis.
In their second phone conversation in the past six days, Obama outlined the terms of a diplomatic "off-ramp" that US officials are promoting.
Under terms of the deal, Russia would pull back troops to bases in Crimea, allow international monitors in to ensure the rights of ethnic Russians are respected and consent to direct talks with Ukraine officials.
"President Obama indicated that there is a way to resolve the situation diplomatically," the White House said in a statement.
US President Barack Obama spoke to Russian President Vladimir Putin for an hour to discuss the situation in Ukraine.
"President Obama emphasised that Russia’s actions are in violation of Ukraine’s sovereignty and territorial integrity, which has led us to take several steps in response, in coordination with our European partners," the White House said.
Former US Secretary of State Hillary Clinton tried to clarify comments that left the impression she had compared Russian President Vladimir Putin to Nazi dictator Adolf Hitler.
In an appearance at the University of California, Clinton said: "The claims by President Putin and other Russians that they had to go into Crimea ... because they had to protect the Russian minorities.
"That is reminiscent of claims that were made in the 1930s when Germany under the Nazis kept talking about how they had to protect German minorities in Poland and Czechoslovakia".
"I just want everybody to have a little historic perspective - I'm not making a comparison certainly, but I am recommending that we perhaps can learn from this tactic that has been used before".
The US President Barack Obama said "Russia's actions in Ukraine is not a sign of strength, but a signal that neighbouring countries have deep concerns about Russian meddling."
"President Putin seems to have a different set of lawyers making a different set of interpretations," Mr Obama said. "But I don't think that's fooling anybody."
Speaking in Washington, Mr Obama said that if Ukraine has legitimate election, there "should be no question that Ukrainian people are capable of governing themselves."
Russia's President Vladimir Putin has reportedly ordered troops taking part in military exercises near the country's western borders "to return to base".
Russian news agencies quoted Kremlin spokesman Dmitry Peskov as saying the exercises, which Moscow denied were linked to events in Ukraine, had been a success.