WASHINGTON, March 1 -- U.S. President Barack Obama, in lengthy talks with Russian President Vladimir Putin over the phone on Saturday, voiced "deep concern" over Russia's "clear violation" of Ukrainian sovereignty and territorial integrity.

Obama called for Russian forces to be withdrawn back to bases in Crimea, an autonomous republic in Ukraine but a focal point now in the country's ongoing crisis.

In his 90-minute conversation with Putin, Obama "expressed his deep concern over Russia's clear violation of Ukrainian sovereignty and territorial integrity" and condemned "Russia's military intervention into Ukrainian territory," the White House said in a readout of the talks.

The phone conversation came after Russia's parliament authorized Putin to use military forces to protect Russian interests in Ukraine earlier in the day.

Putin's spokesman, however, said the president has not yet decided on the use of military forces in Ukraine despite winning the green light, and he would make decisions depending on how the situation evolves.

Ukraine's Interim President Oleksandr Turchynov on Friday appealed to Putin to stop Russia's "naked aggression" and withdraw from the Crimea peninsula in southern Ukraine, where Russia has its Black Sea Fleet based.

"The United States calls on Russia to de-escalate tensions by withdrawing its forces back to bases in Crimea and to refrain from any interference elsewhere in Ukraine," the White House said.

Obama, in a hastily arranged speech on Friday, warned that "there will be costs" for any military intervention in Ukraine.

In a move meant to punish Russia, Obama told Putin on Saturday that his administration will suspend "upcoming participation" in preparatory meetings for the Group of Eight summit to be hosted by Russia in its Black Sea resort of Sochi.

"Going forward, Russia's continued violation of international law will lead to greater political and economic isolation," the White House said.

Tensions flared up in Crimea following the dismissal of Ukraine's pro-Russian President Viktor Yanukovych a week ago by a parliament controlled by West-leaning opposition, who favor integration with the European Union instead of closer ties with Russia.

In his phone talks with Putin, Obama suggested sending international observers to Ukraine, under the auspices of the UN Security Council or the Organization for Security and Cooperation in Europe, to address Russia's concern about the treatment of ethnic Russian and minority populations in Ukraine.

The American leader urged "an immediate effort" to initiate a dialogue between Russia and the Ukrainian government, saying Washington "is prepared to participate."

Obama's national security team met on Saturday to discuss potential policy options in response to events unfolding in Ukraine, but both Obama and Vice President Joseph Biden were absent.

On Saturday, Obama also spoke to French President Francois Hollande and Canadian Prime Minister Stephen Harper over the phone, in which the trio voiced "grave concern" over Russia's intervention in Ukraine, saying Ukraine's "sovereignty and territorial integrity" must be respected, the White House said.

U.S. Defense Secretary Chuck Hagel expressed "deep concern" about Russia's "military intervention" in Ukraine as well, telling his Russian counterpart Sergei Shoigu by the phone on Saturday that Russia "risks further instability" in the region, isolation and an escalation that would threaten European and international security "without a change on the ground."