(Recasts lead, adds fresh Kerry quotes, context)
By Will Dunham
WASHINGTON, March 2 (Reuters) - U.S. Secretary of State John Kerry on Sunday condemned Russia's "incredible act of aggression" in Ukraine and threatened economic sanctions by the United States and allies to isolate Moscow, but called for a peaceful resolution to the crisis.
"You just don't in the 21st century behave in 19th century fashion by invading another country on completely trumped up pre-text," Kerry told the CBS program "Face the Nation."
The Ukraine crisis has taken already strained U.S.-Russian relations to new lows. Kerry did the rounds of the Sunday morning television news shows to emphasize the Obama administration's condemnation of Russia's moves.
Russia still has "a right set of choices" that can be made to defuse the crisis, Kerry said. Asked on the ABC program "This Week" if the United States has "any military options on the table" to address the crisis, he said that President Barack Obama "has all options on the table."
However, he added, "The hope of the United States and everybody in the world is not to see this escalate into a military confrontation. That will not serve the world well, and I think everybody understands that."
He told the NBC program "Meet the Press," "We want a peaceful resolution through the normal processes of international relations."
Putin won permission from his parliament on Saturday to use military force to protect Russian citizens in Ukraine, ignoring warnings from Obama and other Western leaders. Russian forces have already bloodlessly seized Crimea - an isolated Black Sea peninsula where Moscow has a naval base.
"It's an incredible act of aggression. It is really a stunning, willful choice by President (Vladimir) Putin to invade another country. Russia is in violation of the sovereignty of Ukraine. Russia is in violation of its international obligations," Kerry said.
'BROAD ARRAY OF OPTIONS'
Kerry said Obama told Putin in a 90-minute phone call on Saturday "that it was imperative to find a different path, to roll back this invasion and un-do this act of invasion."
Kerry said G8 nations and some other countries are "prepared to go to the hilt to isolate Russia" with a "broad array of options" available.
"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."
Kerry mentioned visa bans, asset freezes, trade isolation, investment changes as possible steps, adding: "American businesses may well want to start thinking twice about whether they want to do business with a country that behaves like this."
"There are very serious repercussions that can flow out of this. There are a broad array of options that are available, not just to the United States but to our allies," Kerry added.
Kerry also called on the U.S. Congress to work with the Obama administration on an economic package to assist Ukraine.
Kerry's comments came amid a chorus of condemnation from Washington and its allies.
Ukraine has asked for help from NATO, Britain and the United States, as co-signatories with Moscow to a 1994 accord guaranteeing Ukraine's security after the breakup of the Soviet Union. Ukraine's security council has ordered the general staff to put all armed forces on highest alert.
Kerry said the United States is "absolutely prepared" to boycott a scheduled G8 meeting in Sochi, Russia, in June. The city also hosted the Winter Olympic Games last month.
Obama canceled a visit to Moscow last September to protest Putin's refusal to help rein in Syrian President Bashar Assad in that country's civil war, although he did attend a G20 summit in St. Petersburg.
The White House said on Saturday the United States will suspend participation in preparatory meetings for the Sochi summit. Kerry said recent events "put at question Russia's capacity to be within the G8."
"If Russia wants to be a G8 country, it needs to behave like a G8 country," he added.
The crisis began in November after Viktor Yanukovich, Ukraine's Russian-backed president who was ousted a week ago, triggered protests by spurning a political and trade deal with the European Union. (Additional reporting by Emily Stephenson, Andy Sullivan and Jim Loney; Editing by Frances Kerry)
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