Kerry said Russian President Vladimir Putin should respect the democratic process through which the Ukrainian people ousted their pro-Russian president and assembled a new government.
But President Barack Obama had pressed his case in a 90-minute phone call Saturday with Putin, calling Russia's actions "a clear violation" of Ukraine's sovereignty, and asking for his forces to pull back, and still the situation only grew more dire Sunday.
Ukraine's new prime minister warned that "we are on the brink of disaster," while hundreds of armed men in trucks and armored vehicles surrounded a Ukrainian military base in Crimea.
Despite the strong words Sunday from America's top diplomat, the Obama administration struggled to find a response that might deter Putin, who contends that the turmoil in its neighbor posed real threats to the life and health of Russian citizens living in Ukraine and that Moscow has the right to protect them.
Sen. Lindsey Graham, R-S.C., suggested suspending Russia's membership in the Group of Eight leading industrial powers for at least a year, "starting right now," and admitting Georgia into NATO in an effort to create "a democratic noose around Putin's Russia."
"Let's challenge him where we can," Graham said, explaining why he also favors reviving plans for a U.S. missile defense system with components in Poland and the Czech Republic.
Russia's "incredible act of aggression" amounts to "a stunning willful choice" by Putin to invade another country on a "trumped-up pretext," Kerry said.
Kerry said he spoke on Saturday with foreign ministers from the G-8 and a few other nations, and "every single one of them are prepared to go to the hilt in order to isolate Russia" because of the invasion.
"They're prepared to put sanctions in place. They're prepared to isolate Russia economically. The ruble is already going down. Russia has major economic challenges. I can't imagine that an occupation of another country is something that appeals to a people who are trying to reach out to the world, and particularly if it involves violence," Kerry said.
Kerry also mentioned visa bans, the freezing of Russian assets, trade and investment penalties. He suggested American companies "may well want to start thinking twice about whether they want to do business with a country that behaves like this."
He said the U.S. was "absolutely prepared" to boycott the G-8 meeting planned for June in Sochi, Russia, site of the just-concluded Winter Olympics, "if we can't resolve it otherwise."
Putin is "not going to have a Sochi G-8. He may not even remain in the G-8 if this continues," Kerry said. Along with the potential loss of foreign business investment and other economic penalties, that would be "a huge price to pay," Kerry said, calling Russia isolated. "That is not a position of strength."
The G-8 countries are the U.S., Britain, Canada, France, Germany, Italy, Japan and Russia.
Kerry also said the administration was ready to provide economic assistance "of a major sort" to Ukraine.
He made clear that a military response to counter Russia's action was unlikely.
"The last thing anybody wants is a military option," he said. "We want a peaceful resolution through the normal processes of international relations."
The U.S. and Europe are not obligated to come to Ukraine's defense because it does not have full-member status in NATO. Broader international action through the United Nations seems all but impossible because of Russia's veto power as a permanent member of the Security Council.
Kerry tried to frame the crisis as broader than U.S. versus Russia or East versus West. "We're not trying to make this a Cold War," he said. It's about Ukrainians "fighting against the tyranny of having political opposition put in jail."
Kerry was interviewed on CBS' "Face the Nation," NBC's "Meet the Press" and ABC's "This Week." Graham appeared on CNN's "State of the Union."