By Steve Holland and Jeff Mason
WASHINGTON, March 6 (Reuters) - President Barack Obama on Thursday ordered sanctions on people responsible for Moscow's military intervention in Ukraine, including travel bans and freezing of their U.S. assets, and said a referendum by the Crimea region to join Russia would violate international law.
U.S. officials said a list of people targeted by the sanctions had not yet been drawn up but Russian President Vladimir Putin is not going to be one of them.
White House spokesman Jay Carney said "I'm not aware of a limit" on how many people could be listed.
Obama signed an executive order aimed at punishing those Russians and Ukrainians responsible for the Russian move into Ukraine's Crimean Peninsula, which has triggered the worst crisis in U.S.-Russian relations since the end of the Cold War.
Escalating the crisis, Crimea's parliament voted to join Russia on Thursday and its Moscow-backed government set a referendum on the decision in 10 days' time.
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 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 in Ukraine and talks between Moscow and Kiev.
"Russia would maintain its 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."
The White House called the order a "flexible tool" aimed at those directly involved in destabilizing Ukraine. Additional steps could be taken if necessary. Any Russian actions in eastern Ukraine would be a potential reason for more measures, a senior U.S. official said.
The State Department is also putting in place visa bans on a number of officials and individuals responsible for or complicit in threatening the sovereignty and territorial integrity of Ukraine.
However, Putin is not one of those to be singled out, a senior administration official said.
"It is an unusual and extraordinary circumstance to sanction a head of state, and we would not begin our designations by doing so," the official said.
LEAVING ROOM FOR DIALOGUE
The Crimean Peninsula in the Black Sea has an ethnic Russian majority and is home to a Russian naval base in Sevastopol.
Obama is attempting to rally global opinion against the Russian move, which Putin says was aimed at protecting ethnic Russians in Crimea. The intervention followed the ouster of Ukraine's pro-Russian president last month.
The United States wants Russian troops to return to their bases in Crimea and for Moscow to allow international monitors into the region to ensure the human rights of ethnic Russians there are protected.
The order was announced as U.S. Secretary of State John Kerry began a meeting with Russian Foreign Minister Sergei Lavrov in Rome and came on the heels of the Crimean parliament's vote to join Russia.
Kerry, speaking in Rome, noted that the sanctions framework was designed to allow talks to go forward.
"We want to be able to continue the intense discussions with both sides in order to try to normalize and end this crisis," he said. "We will absolutely consider if we have to additional steps beyond what we've done but our preference ... is to emphasize the possibilities for the dialogue that can lead to the normalization and defusing of this crisis."
The Obama order targets any assets held in the United States by "individuals and entities" responsible for the Russian military intervention in Ukraine, threatening its territorial integrity or seeking to assert governmental authority over any part of Ukraine without authorization from the Ukrainian government in Kiev.
A senior State Department official said the United States had informed the Europeans beforehand about the sanctions.