Crimea has declared its independence from Ukraine and announced plans to adopt Russian time and currency after Sunday's referendum, in a move set to worsen the diplomatic stand-off between Russia and Western nations.
The United States and the European Union (EU), acting in concert to register a strong response, rolled out sanctions targeting specific Russian officials and Ukrainians.
US President Barack Obama, after signing a new executive order, warned on Monday night that the US stood ready to impose more sanctions, but he also said there was still a path to resolve the Ukraine crisis diplomatically.
The referendum - deemed illegal and illegitimate by the US and its European allies - saw nearly 97 per cent of voters opt to throw in their lot with Russia.
On Monday, the Crimean Parliament adopted a resolution declaring the Black Sea peninsula an "independent sovereign state".
"Crimea appeals to the United Nations and to all countries of the world to recognise it as an independent state," it said, with leaders announcing a series of future measures to break away from Kiev, such as switching to the Russian rouble.
In the Crimean capital of Simferopol and the port of Sevastopol, the majority ethnic Russian community celebrated in the streets, setting off fireworks, waving Russian flags and chanting "Crimea is Russia".
Reactions elsewhere were far from celebratory.
In Washington, Mr Obama ordered financial sanctions and a travel ban to be imposed on 11 people blamed for Russia's move into Crimea. These include top Russian government officials and former Ukrainian president Viktor Yanukovych.
"Today's actions send a strong message to the Russian government that there are consequences for their actions that violate the sovereignty and territorial integrity of Ukraine, including their actions supporting the illegal referendum for Crimean separation," the White House said in a statement.
In a phone call to Russian counterpart Vladimir Putin on Sunday, Mr Obama made clear that the referendum would "never be recognised" by Washington, and urged Mr Putin to find a diplomatic solution to end the crisis.
In Brussels, EU foreign ministers adopted sanctions against 21 Russians and Ukrainians deemed responsible for the referendum, with a promise of more punitive measures in days to come.
"We are trying to send the strongest possible signals to Russia, a signal trying to ensure that they understand the seriousness of the situation," the EU's foreign policy chief Catherine Ashton told reporters before the meeting.
In Kiev, the Ukrainian Parliament approved a presidential decree to mobilise up to 40,000 reservists in a response to the build-up of some 60,000 Russian troops along the border.
Further action from the US or EU may now depend on the outcome of a summit of EU leaders later this week as well as the Russian President's next move.
Mr Putin was scheduled to speak to Russian lawmakers on Tuesday on the Crimea situation, especially on whether or not to accept Crimea as part of the country.
On Monday, global markets closed higher, with investors relieved that the vote had not resulted in violence. The Straits Times Index closed up 18 points.
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