WASHINGTON, March 3 -- U.S. President Barack Obama said on Monday that his administration is examining "a whole series of" economic and diplomatic steps to "isolate" Russia over its refusal to withdraw military forces from the Ukrainian republic of Crimea.

While acknowledging Russia's "strong" historic and commercial ties to Ukraine, the American leader declared that "What cannot be done is for Russia, with impunity, to put its soldiers on the ground and violate basic principles that are recognized around the world."

"And I think the strong condemnation that it's received from countries around the world indicates the degree to which Russia is on the wrong side of history on this," he told reporters at the White House prior to his meeting with visiting Israeli Prime Minister Benjamin Netanyahu.

Obama said Washington is examining "a whole series of steps", both economic and diplomatic, "that will isolate Russia and will have a negative impact on Russia's economy and its status in the world."

He again suggested sending in international monitors to Ukraine, or setting up an international mediation, to address Russia's alleged concerns about treatment of Russian speakers and nationals inside the East European country.

Crimea is now under control of Russian forces following the dismissal of pro-Russian Ukrainian President Viktor Yanukovych on Feb. 22 by a parliament controlled by West-leaning opposition, who favor integration with the European Union instead of closer ties with Russia.

Russian President Vladimir Putin told Obama over the phone on Saturday that Russia retains the right to protect its interests and Russian speakers living in Ukraine if violence spreads in eastern Ukrainian regions and Crimea, where Russia has its Black Sea Fleet based.

Sergei Naryshkin, speaker of Russia's State Duma or the lower house, said on Monday that there is no need yet to use Russia's " right" to launch military action in Ukraine after Putin won parliament approval on Saturday to send Russian forces to Ukraine.

A senior U.S. official told reporters via teleconference on Sunday that the Russian forces were now "in complete operational control of the Crimean peninsula," while another said Russia had moved 6,000 airborne and ground troops into Crimea.

Washington and its allies have already decided to suspend preparations for the Group of Eight summit slated for June in Russia's Black Sea resort of Sochi.

"You can expect that there would be further follow-up on that," Obama said. "We're taking a look at a whole range of issues that John Kerry mentioned yesterday."

The U.S. secretary of state, who is scheduled to leave for Kiev, Ukraine's capital, later Monday, suggested visa bans, asset freezes and trade and business penalties against Russia.

Jennifer Psaki, Kerry's spokeswoman, said Monday that there is not any time frame for the sanctions to be put in place, but Washington is working "in lockstep" with its European allies.

"We're looking at a broad range of options, whether that's individuals, whether that's institutions, whether that's officials, those are all under consideration," she told reporters via teleconference.