Published: Jul 15, 2014 3:55 PM EDT

WASHINGTON (AP) - The United States is considering imposing unilateral sanctions on Russia over its threatening moves in Ukraine, a shift in strategy that reflects the Obama administration's frustration with Europe's reluctance to take tougher action against Moscow, according to U.S. and European officials.
    
Until now, the U.S. has insisted on hitting Russia with penalties in concert with Europe in order to maximize the impact and present a united Western front. The European Union has a far stronger economic relationship with Russia, making the 28-nation bloc's participation key to ensuring sanctions packages have enough teeth to deter Russia.
    
But those same economic ties have made Europe fearful that tougher penalties against Russia could boomerang and hurt their own economies. After weeks of inaction, the officials say the U.S. is now prepared to move forward alone if EU officials fail to enact strong sanctions during a meeting Wednesday in Brussels.
    
The U.S. official cautioned that no final decisions would be made until after the European meeting and said the administration's preference was still to coordinate punishments with Russia. The officials insisted on anonymity because they were not authorized to discuss the matter publicly by name.
    
The White House's willingness to punish Russia without European backing comes as the Obama administration faces criticism that its repeated warnings about tougher sanctions are little more than empty threats.
    
"Sometimes I'm embarrassed for you, as you constantly talk about sanctions and yet, candidly, we never see them put in place," Sen. Bob Corker, R-Tenn., said during a Senate hearing on Ukraine with administration officials last week.
    
The U.S. and Europe have levied coordinated sanctions on Russian individuals and companies connected to Moscow's alleged destabilization in Ukraine. But those penalties have had little impact in stopping a pro-Russian insurgency in eastern Ukraine.
    
Obama and European counterparts have vowed to take even broader sanctions targeting Russia's lucrative energy and defense sectors, as well as access to financial markets, if Moscow failed to quell tensions with Ukraine. But it is unclear what the new package of U.S. sanctions would include.
    
During a Group of Seven meeting in Brussels in early June, Western leaders warned Russian President Vladimir Putin those penalties could be levied within a month if Russia did not meet specific conditions, including recognizing the results of Ukraine's May 25 election and start a dialogue with President Petro Poroshenko, ending support for the pro-Russian insurgency in eastern Ukraine and stopping the flow of arms across the Russian border.
    
The end-of-June deadline the West outlined for Putin came and went with little follow-through from Russia, yet no penalties were levied by the U.S. and Europe.
    
Heather Conley, director of the Europe program at the Center for Strategic and International Studies, said the West's failure to follow through on its threat of sector sanctions has raised a "credibility question" for the Obama administration.
    
"I think the bluff has now been fully called," Conley said.
    
If Obama moves forward with unilateral sanctions, he'll face opposition from the private sector. U.S. businesses have been pressing the administration to hold off on sanctions that could put them at a disadvantage in the global economy.
    
"It's not clear to us that breaking commercial ties with the Russia partners, consumers gets anyone to where they want to be," said Gary Litman, vice president for Europe and Eurasia at the U.S. Chamber of Commerce.
    
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Associated Press writers Matthew Lee in Washington and John-Thor Dahlburg in Brussels contributed to this report.

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