The U.S. said further sanctions are ready to be deployed, while Russia's foreign minister accused the U.S. of "running the show" in Ukraine.
The Ukraine crisis has raised fears that gas supplies flowing to several European countries via Ukraine could be disrupted.
U.S. concerns about the global economy, a weakened ruble and the interdependent nature of key industries may be why Russia isn't feeling the heat.
Russian President Vladimir Putin has consistently denied that Russian forces are stationed in eastern Ukraine.
The U.S. will consider more sanctions soon if Russia doesn't move to implement an agreement to ease tensions in Ukraine.
Less than a week after an agreement to resolve the crisis in Ukraine, new violence has been reported in the country's east section.
So far, pro-Moscow separatist gunmen have shown no sign of surrendering government buildings they have seized.
Earlier, President Vladimir Putin said Russia would give Ukraine a month to start paying off the more than $2 billion it owes for natural gas.
Bank of Russia has blocked certain Ukrainian banks from operating in Crimea, leaving residents with little or no access to banking services.
"We do not connect the economy with the political process," insists the Russian president.
Despite an initial agreement by Russia, Ukraine and the West, agitators refuse to lay down their arms and vacate government buildings.
Funds reported to reduce exposure to risk in Russia.
The prominent oligarch and recently appointed governor is putting his money where his mouth is.
Ukrainian, Russian and Western diplomats try to quell deepening unrest in Ukraine, but on the ground, the situation remains tense.
Kiev fears that the Russian leader will use any violence as a pretext to launch an invasion.
Separatists drove six armored personnel carriers into the town of Slaviansk to waves and shouts of "Russia! Russia!"
The European Union has broadened its sanctions against Russia while the U.S. is “seriously considering" adding more sanctions.
Gunfire could be heard from the airfield at the town of Kramatorsk in eastern Ukraine; Ukrainian troops were seen disembarking from helicopters.
European Union diplomats said there was little prospect of a special summit to discuss additional sanctions because positions are so far apart.
The most serious East-West crisis since the end of the Cold War shows no signs of de-escalating.
Russia's intervention in Ukraine has Georgians worried about another Russia move - this time to the critical Caucuses land bridge.
Separatist groups that favor Russia have taken over Ukrainian government buildings in Donetsk, Lugansk, Kharkov and Slavyansk.