Kerry visits Kiev protest sites
American aid is on the way, John Kerry promised crowds in Kiev as he visited sites where more than 80 anti-government protesters were killed last month.
The US Secretary of State met the new government's acting president, prime minister, foreign minister and top parliamentary officials.
Speaking to reporters afterwards, Mr Kerry said the US is looking for ways to de-escalate the mounting tensions.
"It is clear that Russia has been working hard to create a pretext for being able to invade further," he said.
"It is not appropriate to invade a country, and at the end of a barrel of a gun dictate what you are trying to achieve. That is not 21st-century, G-8, major nation behaviour."
Mr Kerry made a pointed distinction between the Ukrainian government and Russian president Vladimir Putin's.
"The contrast really could not be clearer: determined Ukrainians demonstrating strength through unity, and the Russian government out of excuses, hiding its hand behind falsehoods, intimidation and provocations.
"In the hearts of Ukrainians and the eyes of the world, there is nothing strong about what Russia is doing."
He said the penalties against Russia are "not something we are seeking to do, it is something Russia is pushing us to do".
President Barack Obama said his administration's push to punish Mr Putin put the U.S. on "the side of history that, I think, more and more people around the world deeply believe in, the principle that a sovereign people, an independent people, are able to make their own decisions about their own lives.
"And, you know, Mr. Putin can throw a lot of words out there, but the facts on the ground indicate that right now he is not abiding by that principle."
Mr Obama also spoke for more than an hour yesterday with German chancellor Angela Merkel, who has been in contact with Mr Putin in recent days and whose country has deep economic ties with Russia.
The Obama administration announced a 1 billion dollar (£600 million) energy subsidy package in Washington as Mr Kerry was arriving in Kiev.
The fast-moving developments came as the US readied economic sanctions amid worries that Moscow was ready to stretch its military reach further into the mainland of the former Soviet republic.
Mr Kerry headed straight to Institutska Street at the start of a visit intended to bolster the new government that took over just a week ago when Ukraine president Viktor Yanukovych fled.
Mr Kerry placed a bouquet of red roses, and twice the Roman Catholic secretary of state made the sign of the cross at a shrine set up in memory of protesters who were killed during mid-February riots.
"We're concerned very much. We hope for your help, we hope for your assistance," a woman shouted as Mr Kerry walked down a street lined with tyres, barbed wire and other remnants of the barricades that protesters put up to try to keep Mr Y ukovych's forces from reaching nearby Maidan Square, the heart of the demonstrations.
The Ukraine government continued to grapple with a Russian military takeover of Crimea, a strategic, mostly pro-Russian region in the country's south-east, and Mr Kerry's visit came as Mr Putin said he would not be deterred by economic sanctions imposed punitively by the West.
Ukraine foreign minister Andrii Deshchytsia told reporters that Ukraine was in a much stronger position today than it was even a week ago, having rallied the support of the US and the West.
He said it is unlikely Kiev will ever go to war to prevent Russia from annexing Crimea but said doing so would not be necessary, describing the economic penalties and diplomatic isolation more painful to Russians than bullets would be.
US officials travelling with Mr Kerry said the Obama administration is considering slapping Russia with economic sanctions as soon as this week.
Members of Congress say they are preparing legislation that would impose sanctions as well.
Officials said the sanctions could be implemented in tiers, with an initial round of penalties targeted at individuals the US says were involved in the ousted Ukrainian government's corrupt activities.
Mr Putin is almost certain to be excluded from those penalties, the officials said, adding that it is rare for the US to directly target a head of state with them.
As Mr Kerry arrived, the White House announced the package of energy aid, along with training for financial and election institutions and anti- corruption efforts.
Additionally, the officials said, the US has suspended what was described as a narrow set of discussions with Russia over a bilateral trade investment treaty.
It is also going to provide technical advice to the Ukraine government about its trade rights with Russia.
Mr Putin pulled his forces back from the Ukrainian border yesterday, yet said that Moscow reserves the right to use all means to protect Russians in the country but hopes it does not have to.
He declared that Western actions were driving Ukraine into anarchy and warned that any sanctions the West might place on Russia for its actions there will backfire.
Mr Putin said he still considers Mr Yanukovych to be Ukraine's leader and hopes Russia will not need to use force in predominantly Russian-speaking eastern Ukraine.