President Barack Obama on Thursday, March 6 ordered sanctions on "people responsible for Moscow's military intervention in Ukraine's Crimea Peninsula, including travel bans and freezing of their U.S. assets", and said a referendum by the region to join Russia would violate international law, according to Reuters.

U.S. officials said a list of people targeted by the sanctions had not yet been drawn up but that Russian President Vladimir Putin was not going to be one of them. White House spokesman Jay Carney said he was not aware of a limit on the number of people listed.

Obama spoke to Putin for an hour on Thursday and said the situation could be solved diplomatically in a way that addressed the interests of Russia, Ukraine and the international community, the White House said.

It said Obama spoke later with Japan Prime Minister Shinzo Abe and the two men agreed Russia's actions were a "threat to international peace and security."

Separately, the U.S. House of Representatives overwhelmingly passed a bill backing loan guarantees for the new government in Kiev. The U.S. Senate is expected to consider a similar bill backing $1 billion in loan guarantees next week.

Obama signed an executive order aimed at punishing those Russians and Ukrainians responsible for the Russian military incursion into Crimea, which has triggered the worst crisis in U.S.-Russian relations since the end of the Cold War.

Escalating the crisis, Crimea's parliament on Thursday voted to join Russia and its Moscow-backed government set a referendum on the decision in 10 days.

Obama, appearing in the White House press room hours after signing the order, said the U.S. sanctions were meant to impose costs on Russia for its actions. He said the international community was acting together and warned that a referendum in Crimea would violate international law as well as the Ukrainian constitution.

"Any discussion about the future of Ukraine must include the legitimate government of Ukraine," Obama said. "In 2014, we are well beyond the days when borders can be redrawn over the heads of democratic leaders."

Obama and administration officials emphasized that the U.S. sanctions could be adjusted or additional steps taken as Russian behavior changed.

"While we take these steps, I want to be clear that there is also a way to resolve this crisis that respects the interests of the Russian Federation, as well as the Ukrainian people," the president said, calling for international monitors to be allowed into Ukraine as well as direct talks between Moscow and Kiev.

"Russia would maintain its (military) basing rights in Crimea, provided that it abides by its agreements and respects Ukraine's sovereignty and territorial integrity. And the world should support the people of Ukraine as they move to elections in May," he said, calling that the "path to de-escalation."

Obama made the same argument in his call with Putin.

"President Obama emphasized that Russia's actions are in violation of Ukraine's sovereignty and territorial integrity, which has led us to take several steps in response, in coordination with our European partners," the White House said in a description of the call.