Following the calls, a Downing Street spokesperson said:
Earlier this afternoon, the Prime Minister and President Obama talked about Ukraine again. They discussed events of recent days, including the situation on the ground in Crimea and the rest of the Ukraine, the outcome of the European Council and the US measures.
They agreed that there is still an opportunity for Russia to resolve the situation diplomatically by engaging in direct talks with the Ukrainians, returning Russian troops to their bases in Crimea and working with the rest of the international community to support free and fair elections in Ukraine in May. We should all work together to persuade President Putin to choose this diplomatic path out of the crisis. Both the Prime Minister and the President firmly believe that the proposed referendum in Crimea would be illegal and that any attempt to legitimise it would result in further consequences for Russia.
The Prime Minister has also spoken to the Canadian Prime Minister, Stephen Harper, about the situation. They both agreed that President Putin still had the opportunity to de-escalate the situation. They also discussed the need for the International Monetary Fund to lead on a package of financial assistance to the Ukrainian government to help provide economic stability in the months ahead and to ensure that the new Ukraine government implements the necessary economic reforms.
We expect the Prime Minister to remain in close touch with other G8 leaders on this issue in the coming days.