President Barack Obama warned Monday that the United States was planning a string of economic and diplomatic sanctions to “isolate” Russia if it does not reverse its incursion into Ukraine.

“Russia is on the wrong side of history,” Obama said, declaring that the world was all but united in viewing Moscow’s dispatch of troops to Crimea as a violation of international law.

A day before Secretary of State John Kerry arrives in Kiev to show US backing for Ukraine’s right to chart its own future, Washington expanded on the “costs” Russia may have to pay for its action.

It pointed to the sharp decline of the ruble as evidence Russia was already paying a heavy price and Obama asked Congress to put an economic support package for Ukraine on the top of its agenda.

“What cannot be done is for Russia, with impunity, to put its soldiers on the ground and violate basic principles that are recognized around the world,” Obama said.

“What we are also indicating to the Russians is that if, in fact, they continue on the current trajectory that they’re on, that we are examining a whole series of steps — economic, diplomatic — that will isolate Russia.”