U.S. President Barack Obama and European leaders, in a show of solidarity, agreed on Monday to impose a wider set of sanctions against Russia's financial, defense and energy sectors in the wake of the shootdown of a passenger jet over Eastern Ukraine, a top Obama aide said.
It is still unclear "exactly who pulled the trigger" to down the Malaysian jet, but he said Russia is culpable.
The coordinated measures come as the United States warned of a Russian troop buildup along the border with eastern Ukraine and the shipment of new sophisticated weapons to pro-Russian separatists.
EU diplomats reached a preliminary deal on Monday on a list of people, including associates of Russian President Vladimir Putin, and firms to be subject asset freezes as part of tougher measures over Russia's actions in Ukraine, EU diplomats said.
The new list of names is expected to be published on Tuesday or Wednesday and is in addition to 87 people and 20 organizations already subject to EU sanctions.
The three diplomats speaking on condition of anonymity said they could not give full details, but the persons targeted included people and companies, who are supporting or benefit from destabilization of Crimea and Russia's annexation of Crimea.
"The list includes individuals, cronies and entities,'' one diplomat said. Another said the list was "subject to some legal refinement'' and would be signed off on Tuesday when EU diplomats continue talks.
The new sanctions, which Obama and leaders of Germany, Britain, France and Italy discussed in a rare five-way conference call by video and phone, are aimed at increasing the pressure on Russian President Vladimir Putin.
Obama met with German Chancellor Angela Merkel, Prime Minister David Cameron of the United Kingdom,French President Francois Hollande and Italian Prime Minister Matteo Renzi, Hollande said in a statement, translated via Google Translate.
"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,'' said Tony Blinken, a national security adviser to Obama.
Obama and top aides have been working behind the scenes to convince European allies to impose sanctions against Russia that are on par with U.S. sanctions. Europe's response to Russian aggression in Ukraine has been more tepid than that of the United States because its economy is more entwined with Russia's.
Blinken told reporters existing sanctions have hurt Russia's economy, but have not been enough to force Putin to back off.
Instead, Blinken said Russia has increased the supply of heavy weapons to the separatists.
"We've seen convoys of tanks, multiple rocket launchers, artillery, and armored vehicles. There's evidence it's preparing to deliver even more powerful multiple rocket launchers,'' Blinken said.
SA-11 launchers are still believed to be in Ukraine, potentially in separatist hands, he said.
A Russian troop buildup on the border is also raising concerns that Russia could create a pretext for an incursion into eastern Ukraine to support the increasingly embattled rebels who have been blamed for shooting down a Malaysian passenger plane July 17.
"We've seen a significant rebuild up of Russian forces along the border, potentially positioning Russia for a so-called humanitarian or peacekeeping intervention in Ukraine," he said.
The leaders also discussed next steps on the situation in the Middle East, Iraq and Libya.
U.S. Vice President Joe Biden will meet with Ukraine's Foreign Minister Pavlo Klimkin at the White House later on Monday, the White House said in a statement.
—By Reuters. CNBC.com contributed to this report.