The Obama administration and Congress are moving on several fronts to try and calm the Ukraine stand-off -- and pressure Russia to cooperate -- ahead of a looming Crimea referendum which could further inflame the crisis.
President Obama, in a diplomatic snub at Russia, met Wednesday with Ukrainian Prime Minister Arseniy Yatsenyuk at the White House.
Sitting side by side in the Oval Office with Yatsenyuk, Obama said he hoped last-ditch diplomatic efforts might lead to a "rethinking" of Sunday's referendum on whether Crimea should join Russia. If the vote does occur, Obama said, "We will not recognize any referendum that goes forward."
He warned that Russia could face "costs" and blasted the "slapdash election" as one being done at "the barrel of a gun."
Yatsenyuk said Ukraine will "never surrender" in the fight over its territory. "Ukraine is and will be part of the Western world," Yatsenyuk said in English.
A bipartisan group of senators also said they plan to travel to Ukraine on Thursday to meet with members of the interim government.
The developments come ahead of a scheduled Crimea vote on Sunday on whether to split off from Ukraine and join Russia. The United States and its top allies are presenting a united front against that referendum, arguing that the results will not be legitimate.
But, applying a carrot-and-stick approach, the U.S. is both courting and pressuring Russia. As Obama met Wednesday with the new Ukrainian prime minister, Secretary of State John Kerry announced plans to travel to London to again meet with Russia's foreign minister in the hopes of calming the Ukraine crisis ahead of Sunday's vote.
"Nothing justifies a military intervention that the world has witnessed," Kerry told a House panel on Wednesday morning. He said he would travel Thursday evening to London in order to meet Friday with Russia's Sergei Lavrov, and present a series of "choices" for the Russian government.
Kerry argued that there are ways to resolve the stand-off and protect Russia's interests in the region. He added: "We will do what we have to do if Russia cannot find a way to make the right choices here."
He was referring to sanctions and other steps the U.S. and other countries are poised to take. The situation could become more dire if not resolved soon, as Crimea prepares to vote Sunday on whether to split off from Ukraine and become part of Russia.
In anticipation of that vote, the G7 world leaders said Wednesday they will not recognize that decision. The leaders of the seven nations, including the United States, said in a statement that any attempt by Russia to change the status of Crimea would be a violation of international law and a referendum to annex Crimea "would have no legal effect."
"Given the lack of adequate preparation and the intimidating presence of Russian troops, it would also be a deeply flawed process which would have no moral force. For all these reasons, we would not recognize the outcome," the statement said. The statement was from Canada, France, Germany, Italy, Japan, Britain and the United States, along with the European Council and the European Commission.
The leaders released the statement as members of Congress weigh some of the most significant sanctions on Russia since the end of the Cold War.
The Senate Foreign Relations Committee on Wednesday advanced sanctions legislation that would pressure Russian President Vladimir Putin to pull Russian troops out of Crimea.
It authorizes $1 billion in loan guarantees to Ukraine's new government and allows the Obama administration to impose economic penalties on Russian officials responsible for the intervention in Crimea or culpable of gross corruption. All Democrats supported the measure. Republican objections include how the U.S. will pay for the loan guarantees and provisions in the bill expanding the lending authority of the International Monetary Fund.
House Republicans are pushing their own bill.
Washington has been more strident in its measures thus far against Russia than its allies have, with European countries from Germany to Britain fretful that a sudden deterioration in relations with Moscow could be harmful for their manufacturing exporters and financial institutions.
"Putin has miscalculated by playing a game of Russian roulette with the international community, but we refuse to blink, and will never accept this violation of international law," said Sen. Bob Menendez, a New Jersey Democrat, who introduced the legislation. "Ukraine is confronting a menacing threat challenging its very existence and in t heir hour of need, we firmly stand with the Ukrainian people to choose their own destiny without Russian interference."
The House overwhelmingly backed providing only the assistance to Ukraine last week and passed a resolution calling for sanctions on Russia Tuesday. Neither included language on the IMF, which the United States, European countries and others are working with to provide billions of dollars in loans to Ukraine's cash-depleted authorities.
Putin and other Russian officials have threatened retaliation for any Western punishment over Russia's occupation of Ukraine's Crimean peninsula. But with the U.S. and its European allies ruling out military options, a broad consensus has emerged among the Obama administration and Democratic and Republican lawmakers that sanctions are the strongest option available.
Tensions are increasing ahead of the Russian-backed referendum this weekend in Crimea, where voters may declare the territory independent and propose becoming a Russian state. The U.S. and the European Union have both declared the vote as illegitimate.
The Associated Press contributed to this report