International powers are to meet in London tomorrow to work on drawing up a list of Russian figures who could face asset freezes and travel bans if Moscow fails to de-escalate the current crisis over Ukraine, Prime Minister David Cameron has told MPs.
In a statement to the House of Commons on last week's emergency European summit on the Ukraine crisis, Mr Cameron acknowledged that sanctions against Russia could have consequences for the UK and its European Union partners.
But he warned: "Britain's own security and prosperity would be at risk if we allow a situation where countries can just flout international rules without incurring consequences."
The Prime Minister met German Chancellor Angela Merkel in Hanover last night to discuss the ongoing crisis, which has seen troops loyal to Moscow occupying the Crimean peninsula after a revolution ousted pro-Russian president Viktor Yanukovych from power.
Mr Cameron and Mrs Merkel issued a warning to Russia of "further consequences" if Moscow attempts to legitimise any attempt by Crimea to break away from Ukraine following a referendum scheduled for March 16.
The Prime Minister and German Chancellor restated their view that the proposed vote on whether the southern Ukrainian peninsula should join the Russian Federation would be illegal.
Last Thursday's emergency summit in Brussels agreed a three-stage process by which the EU will respond to Russia's actions in Ukraine, Mr Cameron told MPs.
As a first response, preparations for the G8 summit in the Russian resort of Sochi were suspended, ministers and members of the Royal Family cancelled planned trips to the Winter Paralympics, work on a more liberal EU visa regime for Russians was halted and the UK began a review of all Government business and arms export licences.
If Russia fails to come to the negotiating table with the government of Ukraine within days in a new Contact Group, the EU is ready "rapidly" to implement a second phase of action, including asset freezes and travel bans on key figures in Vladimir Putin's administration, said Mr Cameron.
"We are working are closely with our American, European and other international partners to prepare a list of names and these sanctions - plus the measures already agreed against Yanukovych and his circle - will be the focus of a meeting here in London tomorrow with key international partners," the Prime Minister told MPs.
And if Russia took "further unacceptable steps" to destabilise Ukraine, the European Council agreed that there would be " additional and far reaching consequences" covering a broad range of economic areas.
Mr Cameron said: "Such sanctions would have consequences for many EU member states, including Britain
"But as I argued at the meeting, the costs of not standing up to aggression are far greater.
"Britain's own security and prosperity would be at risk if we allow a situation where countries can just flout international rules without incurring consequences."
Denouncing recent events in Ukraine as "completely indefensible", the Prime Minister said: "Its territorial integrity has been violated, and the aspirations of its people to chart their own future are being frustrated."
The 28 nations of the European Union were "clear and united" that Russia's actions were "in flagrant breach of international law and will incur consequences"
But Mr Cameron added: "There is still an opportunity for Russia to resolve this situation diplomatically.
"They should engage in direct talks with the Ukrainians, return Russian troops to their bases in Crimea, withdraw their support for this illegal and unconstitutional referendum in Crimea, and work with the rest of the international community to support free and fair elections in Ukraine in May.
"I am not interested in a tug of war. Ukraine should be able to choose its own future and act as a bridge between Russia and Europe."
In a reference to the period since the end of the Second World War, Mr Cameron said: " In Europe we have spent the last 70 years working to keep the peace - and we know from history that turning a blind eye when nations are trampled over stores up greater problems for the longer term.
"We must stand up to aggression, uphold international law, and support the Ukrainian government and the Ukrainian people who want the freedom to choose their own future."
He repeated his view that it would be "completely wrong" for the G8 group of eight of the world's leading economies to gather in Russia under current circumstances. But in response to questioning from Labour leader Ed Miliband, he indicated that he would not rule out the other seven members - Britain, the US, France, Germany, Japan, Canada and Italy - meeting as a G7.
Mr Cameron made his statement hours after returning from a two-day visit to Germany, where Ukraine was top of the agenda in talks with Mrs Merkel.
Following the talks, a Downing Street spokesman said: "They both agreed that the priority is to de-escalate the situation and to get Russia to engage in a contact group as swiftly as possible.
"They reiterated their view that the proposed referendum in Crimea would be illegal and that any attempt by Russia to legitimise the result would result in further consequences.
"They also agreed that we must keep working to support the Ukraine government, including identifying how the international community can help to stabilise the economic situation."
Meanwhile, Foreign Secretary William Hague suggested the next phase of the European response could begin when ministers gather again on Monday ahead of next week's scheduled EU leaders' summit in Brussels. The crisis over Ukraine could lead to a long-term recasting of the EU's relations with Russia, he suggested.
After holding talks with Polish counterpart Radoslaw Sikorski in London, Mr Hague said: "Long term, it means that Europe needs to talk about how we recast our approach, including on energy policy, to change the balance of leverage between Russia and the EU."
Mr Sikorsi indicated that Warsaw would favour a 10-day deadline for Russia to come to the table.
"If there is no de-escalation then, within about 10 days, sanctions must be imposed," he said.
"We are ready to work very closely with Russian authorities on creating diplomatic initiatives, a contact group that could help de-escalate the situation.
"But we also have to be clear that if no de-escalation moves happen, or if Russia goes into the Ukraine mainland, or indeed uses its forces in Moldova to do the similar things as are being done in Crimea, the sanctions that we will consider will be much more severe.
"This is a moment of test for the unity of the EU, for the unity of the Nato alliance."
The Ministry of Defence (MoD) said it would deploy an RAF reconnaissance plane over Poland and Romania as part of Nato's efforts to monitor the crisis in Ukraine.
A MoD spokeswoman said that a single RAF plane and pilot would be involved in the mission.
The spokeswoman said: "The North Atlantic Council on Monday decided to employ AWACS (Airborne Early Warning and Control Aircraft) reconnaissance flights over Poland and Romania, as part of the Alliance's efforts to monitor the crisis in Ukraine.
"We have said that the UK will meet all our commitments under the next level of Nato Crisis Response measures.
"As the UK E-3D AWACS (Airborne Early Warning and Control Aircraft) is part of the Nato AWACS Force, then it is only right that the UK undertakes its share of this mission."