WASHINGTON - President Barack Obama told Russian President Vladimir Putin on Saturday that the U.S. may boycott an upcoming economic summit in Russia and threatened further penalties if Moscow did not recall its military forces from Ukrainian territory.
In a 90-minute telephone call, Obama warned Putin that Russia faces "greater political and economic isolation," according to a White House description of the call. The President suggested the United Nations would take action for what he called a "breach of international law."
Obama made the threats as the two leaders publicly clashed over the deepening crisis in the former Soviet state.
Obama warned Friday that "there will be costs" to the Russian military intervention in the Ukrainian region of Crimea, a hot bed of opposition to the newly established, pro-Western transitional government in Kiev. Putin nonetheless sought authorization for military action from the Russian Senate, saying Moscow had a right to protect its military bases in the region.
Obama told Putin on Saturday that the U.S. recognized "Russia's deep historic and cultural ties to Ukraine and the need to protect the rights of ethnic Russian and minority populations within Ukraine." But he urged Putin to engage directly with the interim leaders in Kiev to protect those rights.
Putin's moves have sent the White House scrambling to react. Obama's national security advisers met at the White House on Saturday to devise a response, while Obama dialed up foreign leaders.
The White House has said it is considering diplomatic steps that might underscore Obama's message to Putin. Chief among them is canceling Obama's plans to attend a Group of Eight summit in Sochi, Russia, this year.
A week after violent protests forced Russian-backed President Viktor Yanukovich to abandon power in Kiev, Ukraine's new leaders say Russia is trying to take control of the southern Crimea region, which has a majority ethnic Russian population.
France, Britain and Germany issued calls for de-escalation in Crimea just hours after Obama warned that military intervention in the region would be deeply destabilizing.
Meanwhile, U.S. Defense Secretary Chuck Hagel told his Russian counterpart on Saturday that Moscow's military intervention risked creating an escalation "that would threaten European and international security," the Pentagon said.
"Secretary Hagel stressed that, without a change on the ground, Russia risks further instability in the region, isolation in the international community and an escalation that would threaten European and international security," Pentagon spokesman Rear Adml. John Kirby said in a statement, describing the call with Russian Defense Minister Sergei Shoigu.
British Prime Minister David Cameron said he had told Putin in a phone call on Friday that "there can be no excuse for outside military intervention in Ukraine."
"Everyone must think carefully about their actions and work to lower, not escalate, tension," he said. "The world is watching."
French President Francois Hollande spoke to Putin on Saturday to tell him of his "grave concern" and urge him to "avoid any use of force and to seek a solution to the crisis with the international community," a statement from Hollande's office said.
Hollande urged European countries to take swift and decisive action to find a way out of the crisis in Crimea when their foreign ministers meet in Brussels on Monday.
"Everything must be done to avoid outside intervention and the risk of a highly dangerous escalation," he said.
Hollande also spoke about the situation in Crimea with Obama, German Chancellor Angela Merkel and European Council President Herman Van Rompuy.
No bloodshed followed Yanukovich's overthrow, but Ukraine's new leadership faces a challenge in Crimea, which was part of Russia until 1954.
Ukrainian Prime Minister Arseny Yatseniuk accused Russia on Saturday of sending thousands of troops to the area. Armed men wearing combat uniforms with no identification have taken control of two airports in the area and have taken over the regional parliament in what Kiev describes as an occupation by Moscow's forces.
Putin obtained authorization from the upper house of parliament to send armed forces to Ukraine's Crimea region, although a spokesman said no decision had yet been taken on whether to send them.
British Foreign Secretary William Hague, who travels to Ukraine today to hold talks with the new leadership, urged his Russian counterpart to act to ease tensions and said Russia was posing a potentially grave threat to Ukraine.
Putin told Obama by telephone that Moscow reserves the right to protect its interests and those of people in Ukraine who speak Russian, the Kremlin said.
In a statement posted online, the Kremlin said Obama had expressed concern about the possibility of Russian military intervention in Ukraine.
"In response to the concern shown by Obama about the plans for the possible use of Russia's armed forces on the territory of Ukraine, Putin drew attention to the provocative, criminal actions by ultra-nationalists, in essence encouraged by the current authorities in Kiev," the statement said.
"The Russian president underlined that there are real threats to the life and health of Russian citizens and compatriots on Ukrainian territory."