Even action taken under the auspices of humanitarian support would be viewed as a violation.
Officials say the two sides are talking, despite a press report.
Obama spoke by phone with leaders from France, Germany, Italy and the U.K.
The secretary of State seemed to suggest economic sanctions over Ukraine are coming.
Kerry asks Russia to tone down "escalatory rhetoric" in Ukraine.
Rep. Adam Schiff (D-Calif.) says the U.S. needs to "prepare for the worst."
Russia's ambassador to the U.S. decried an overnight shooting.
Press reports say the U.S. may try to freeze Putin's personal fortunes.
People reported fliers that asked Jews to register with the government.
The exchange appeared to be designed to embarrass the United States.
The leaders of the House Foreign Affairs Committee will travel to Ukraine next week amid signs that...
Power said developments in eastern Ukraine have "all the telltale signs" seen in Crimea.
Sanctions expected to have significant economic ramifications on Russian companies.
"I don't understand why he couldn’t have been part of the debate here at home," she said.
"I used to be a pretty good swimmer. I grew up in Hawaii,” Obama said.
Russian officials have taken several actions that could give them more control.
The founder of Russia’s answer to Facebook announced that he had been fired on Monday.
“Our foreign policy is always a day late and a dollar short," the senator said.
At least two people were killed in an attack in eastern Ukraine on Sunday.
The former NSA contractor said the questioning was intended to expose the Kremlin.
The items include medical supplies, water purification units and generators.
Obama says Russia realizes U.S. military is "significantly superior."
McCain said the attacks over the past few days are “of course” being orchestrated by Putin.
Kerry expressed strong concern that pro-Russian gunmen orchestrated attacks in Ukraine.