WASHINGTON - US President Barack Obama's national security adviser, Susan Rice, said on Sunday it would be a "grave mistake" for Russia to send military forces into Ukraine and that it is not in the interest of Russia, Europe or the United States to see Ukraine split apart.Speaking on the NBC program "Meet the Press," Rice was asked about a possible scenario in which Russia would send forces into Ukraine to restore a government more friendly to Moscow."That would be a grave mistake. It's not in the interests of Ukraine or of Russia or of Europe or the United States to see a country split. It's in nobody's interest to see violence return and the situation escalate," Rice said."There is not an inherent contradiction ... between a Ukraine that has longstanding historic and cultural ties to Russia and a modern Ukraine that wants to integrate more closely with Europe. This need not be mutually exclusive," Rice said following the political upheaval in Ukraine.