Saying that the conflict in Ukraine had "gone on for far too long," Secretary of State John Kerry called on Russia to use its "considerable influence" to make sure investigators had access to the debris field of the downed Malaysia Airlines plane in eastern Ukraine.
The separatists who control that area of Ukraine, said Kerry, "have displayed an appalling disregard for human decency."
Kerry spoke after Dutch and Australian experts abandoned their attempts for a third day in a row to reach the debris field.
CNN reports that the 50-member team was accompanied by monitors from the Organization for Security and Co-operation in Europe, who were unable to leave Donetsk because "there is too much fighting at the moment on and near the route to the disaster site."
Kerry also spoke after the European Union agreed to implement tougher sanctions against Russia.
Reuters reports the deal reached by the EU on Tuesday targets the Russian "oil industry, defense, dual-use goods and sensitive technologies."
"Among the new measures that were discussed are steps that could limit access of Russian banks to European capital markets, which could affect European holders of Russian debt and financial services firms that do business there," Reuters reports.
Meanwhile, the White House said the U.S. could also unveil additional sanctions against Russia as early as today.
"It's precisely because we've not yet seen a strategic turn from Putin that we believe it's absolutely essential to take additional measures, and that's what the Europeans and the United States intend to do this week," Tony Blinken, Obama's deputy national security adviser, told the AP earlier Tuesday.
Kerry, who was speaking alongside the Ukrainian foreign minister in Washington, said he had talked to Russian Foreign Minister Sergey Lavrov, who told him Russia wanted to de-escalate the situation in Ukraine.
However, Kerry said, actions have not shown "a shred of evidence" that Russia wants to end the violence.
Russia Today, the Russian-funded, English-language news service, reports that Lavrov blamed Kiev. If it adhered to a cease-fire agreement, Lavrov said, investigators would have access to the Malaysia Airlines disaster site.