A Downing Street spokesperson said:

The Prime Minister remains gravely concerned about events in Ukraine and is determined to pursue all avenues to reduce tensions and de-escalate a very dangerous situation.

This evening he will speak to President Obama, Polish Prime Minister Tusk and Lithuanian President Grybauskaite.

Earlier today the Foreign Secretary flew to Kiev to meet the new Ukrainian authorities, make clear our support for them, and urge continued restraint.

In current circumstances, the Prime Minister is clear that the focus of our engagement with Russia must be the situation in Ukraine, rather than other normal business. The Foreign Secretary announced earlier today that the UK will not take part in any of the G8 preparatory meetings in Russia planned for this week.

The Prime Minister and Foreign Secretary have also decided that it would be inappropriate for UK ministers to attend the Sochi Paralympics in current circumstances.

The Prime Minister remains fully supportive of our Paralympic athletes’ participation at Sochi.

A stable Ukraine is in the interests of everyone – including the UK. Ukraine is one of the largest countries in Europe and a neighbour of the European Union. Its economic prosperity, security and stability matter. The sovereignty and territorial integrity of Ukraine has been violated and this cannot be the way to conduct international affairs.