US President Barack Obama: 'We will stand with Ukraine'
12 March 2014 Last updated at 20:58 GMT
Western leaders have stepped up pressure on Russia to abandon efforts to annex Ukraine's Crimea region or face sanctions.
President Obama said they "will be forced to apply costs" if Russia does not change course.
He was speaking after holding talks with Ukraine's interim Prime Minister Arseniy Yatsenyuk in Washington.