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President Obama has told Vladimir Putin today's referendum in Crimea "would never be recognised" by the US or the rest of the international community, the White House has said.
The Chilean government has ordered an evacuation of northern parts of the country following an earthquake off its coast.
Crowds chanted "Russia!" at a rally in Simferopol as some preliminary reports show that 96% voted for a union with Russia.
Crimean Prime Minister Sergei Aksyonov led crowds in the city centre:
A magnitude 7.0 earthquake hit the Pacific coast of Chile at a depth of 20.5 miles (32 km), the U.S. Geological Survey said.
The quake was centered 44 miles (70 km) northwest of Iquique, in northern Chile, the USGS said.
There were no immediate reports of injuries or damage.
Sanctions targeted at individuals in Russia will be announced "soon", a senior US official has told NBC.
The US and European countries are both expected to announce additional sanctions tomorrow.
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.
Results from half of the Crimean polling stations show that 95.5% of voters supported union with Russia according to Reuters quoting the Russian state news agency.
Voters were given two options on the ballot paper, union with Russia or greater independence from Ukraine . There was no way to retain the status quo.
At least three people have died and five have been wounded after a suicide bombing in a Lebanese town near the border with Syria, according to Reuters.
The blast happened in the small town of Nabi Osmane, a stronghold of the militant Hezbollah group, which has been fighting alongside forces loyal to Syrian President Bashar al-Assad.