Vladimir Putin has warned he will use "all means" to protect Russian citizens in Ukraine against what he called an "unconstitutional coup".

In his first public comments on the crisis since Ukrainian president Viktor Yanukovych was ousted, Mr Putin said there was no need to use force in Crimea, where tensions between Russian and Ukrainian troops have flared .

But the Russian leader said he reserved the right to use military action there as a "last resort".

Any intervention, he said, would be "legitimate and within the framework of international law".

He also claimed Mr Yanukovych is still Ukraine's president, saying: "As to whether this leadership in Ukraine is legitimate - no, they are not - and I can't say anything about the legitimate status of the so-called acting president in Ukraine. Of course he doesn't have any power in Ukraine."

Mr Putin said Mr Yanukovych fulfilled all conditions of a February 21 agreement with the Ukrainian opposition and effectively "gave up power".

But he claimed that Mr Yanukovych "would have been murdered" if he remained in Ukraine during the unrest and no longer has a political future in the country.

Speaking on elections in Ukraine, Mr Putin said: "If elections are held under such terror as we see now, then we won't recognise them."

British Foreign Secretary William Hague made it clear he had no doubt that the troops in Crimea were acting on orders from Moscow, despite claims by Mr Putin they were "local self-defence forces", during a statement to the House of Commons.

He said: "The suggestion that a president who has fled his country then has any authority whatsoever to invite the forces of a neighbouring country into that country are baseless.

"Russia has also argued that Russian-speaking minorities in the Ukraine are in danger, but no evidence of that threat has been presented.

"The UK's national interest lies in a free, democratic, unified, stable and peaceful Ukraine, able to make its own decisions about its future.

"For that reason it is important there is a clear response to these events and that they are not repeated."

His comments come as US Secretary of State John Kerry arrived in the Ukrainian capital Kiev for talks.

America said on Monday night that any threat by Russia to Ukraine forces would represent a "dangerous escalation" in the crisis and Moscow would be held responsible.

Russia has threatened it could be forced to drop the dollar as a reserve currency and refuse to pay off loans to US banks if sanctions are imposed on it by the US.

Nato will hold more emergency talks on the crisis on Tuesday after Poland requested consultations with its allies on the threat posed by Moscow.

The Russian foreign ministry said Nato's criticism of its actions in Crimea "will not help stabilise" the situation in Ukraine.

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