US President Barack Obama and British Prime Minister David Cameron pledged to maintain diplomatic pressure on Moscow so that the latter change its position towards Ukraine.

"If we allow such fundamental breaches of international law to go unchecked, we will all suffer from the instability that would follow. Our strong and united response has sent an unmistakable message that the international community will not stand by as Russia attempts to destabilize Ukraine," UK The Times quotes a joint Obama-Cameron statement.