(We updated this post at 8:28 p.m. ET.)
The United States and the European Union are threatening Moscow with sanctions over Russia's move to dispatch troops into Ukrainian territory.
During short remarks at the Oval Office, President Obama said the U.S. was examining a wide array of steps that include putting "economic and diplomatic" pressure on Russia.
Obama said the strong condemnation issued by the global community "shows how Russia is on the wrong side of history."
A few hours after those comments, the U.S. announced it was halting any joint military exercises, meetings, port visits and planning conferences with Russia and that it was suspending trade and investment talks with the country.
"The Defense Department is closely monitoring the situation and remains in close contact with the State Department and interagency, along with our Allies, Partners and NATO," Pentagon Press Secretary Rear Adm. John Kirby said in a statement. "We call on Russia to deescalate the crisis in Ukraine and for Russian forces in Crimea to return to their bases, as required under the agreements governing the Russia Black Sea Fleet."
Kirby also said that the U.S. had not changed its military posture in Europe or the Mediterranean.
Reuters reports State Department spokeswoman Jen Psaki told reporters during a conference call on Monday that the U.S. has a broad range of options to impose against Russia if the situation continues to escalate.
"At this point, we are not just considering sanctions. Given the actions Russia is taking, it is likely we will put those in place and we are preparing that," Psaki said.
Psaki was challenged by reporters on what kind of effect sanctions could have.
According to Olivier Knox, who covers Washington for Yahoo, Psaki said U.S. rhetoric is already "having an impact" on Russia's currency and stock market. Knox reports Psaki said the U.S. is not just "talk, talk, talk" on Ukraine.
"We are very much walk, walk, walk," Psaki said.
Meanwhile, Reuters reports that after a meeting today [Monday], European Union foreign ministers agreed they would consider sanctions against Russia, if the crisis continues.
"The EU not only asked Russia to de-escalate the situation in Crimea, but said that if Russia does not do that, the EU would consider imposing sanctions," Polish Foreign Minister Radoslaw Sikorski is quoted as saying.
On Sunday, the State Department announced that Secretary of State John Kerry would arrive in Kiev, the Ukrainian capital, on Wednesday.
"The Secretary will reaffirm the United States' strong support for Ukrainian sovereignty, independence, territorial integrity, and the right of the Ukrainian people to determine their own future, without outside interference or provocation," Psaki said in a written statement.
During his statement, Obama said if Russian President Vladimir Putin is truly interested in protecting Russians in Ukraine, then they should be able to de-escalate the situation.
Obama said he was willing to negotiate the presence of international observers in the country who could protect Russian interests.
Update at 8:05 p.m. ET. U.S. Suspends Military Engagements:
The U.S. is taking two concrete steps this evening as it relates to Russia:
-- CBS News' Mark Knoller reports that the Pentagon says it "put on hold all military-to-military engagements" with Russia.
-- The Wall Street Journal reports that the U.S. has suspended trade and investment talks with Russia. The paper reports:
"U.S. officials in recent months had begun informal negotiations with Russian counterparts in an effort to boost economic ties. Compared with the size of their economies, Russia and the U.S. have a small trade relationship, representing just 1% of U.S. imports and exports from around the world.
'Due to recent events in Ukraine, we have suspended upcoming bilateral trade and investment engagement with the government of Russia that were part of a move toward deeper commercial and trade ties,' said a spokesman for U.S. Trade Representative Michael Froman."
Update at 5:47 p.m. ET. Focused On Getting Troops Out Of Ukraine:
In an interview with All Things Considered, Deputy National Security Adviser Tony Blinken said the U.S. is at the moment focused on getting troops out of Ukraine not getting troops from another country — including the U.S. — into it.
When Melissa Block asked him if the United States was prepared to allow Russia to annex Crimea, Blinken responded:
"Ukraine and its territorial and integrity and its sovereignty is a basic principle that the international community is standing strongly for."
Update at 4:03 p.m. ET. A Dramatic Moment At U.N.:
Just a few moments ago, the U.S. and Russian ambassadors to the United Nations gave the Security Council vastly different accounts of what they think is happening in Ukraine.
Vitaly Churkin said "lives are being threatened" and former Ukrainian President Viktor Yanukovych had sent Putin a letter asking him to use the Russian armed forces to "to establish legitimacy, peace, law and order, stability and defending the people of Ukraine."
People of Russian descent, Churkin said, are facing a "real threat," and the actions of Russia "are fully appropriate."
Samantha Power, the U.S. ambassador to the U.N., said Russia was acting on "imaginary threats." She said Russia's incursion into Crimea is a "violation of international law ... not a protection of human rights."
Despite Russia's "self-serving rhetoric," Power said, "nothing justifies their actions."
She called Russia's incursion "an act of aggression." Like Obama before her, she also gave Russia an out: She said if Russia was concerned about the well-being of Russians in Crimea, the U.S. would support the deployment of international monitors to the region.