Washington: The White House expressed concern Thursday that pro-Russian separatists in Ukraine were using advanced weapons "from the outside" after they shot down an army helicopter killing 12 soldiers.
The downing of the aircraft came amid escalating clashes between Kiev`s forces and separatists in the eastern part of the country, following the election win of chocolate magnate Petro Poroshenko.
"We are disturbed by the ongoing violence in eastern Ukraine, including reports that separatists have shot down a Ukrainian military helicopter," White House spokesman Jay Carney said.
"Now we cannot yet verify the details of these reports, but we are concerned that this indicates separatists continue to have access to advanced weaponry and other assistance from the outside," Carney added, hinting that Russia could be boosting the separatist forces.
Moscow has consistently denied such accusations.
The Mi-8 helicopter gunship was shot out of the sky with a sophisticated surface-to-air missile. Among the dead was a Ukrainian general.
Acting President Oleksandr Turchynov said the weapon used was a Russian man-portable air defense system.
As well as hinting at Russian assistance, Carney voiced concern for a team of Organization for Security and Cooperation in Europe observers being held by separatists in the city of Slavyansk.
"It is unacceptable for observers to be detained, and they should be released immediately. We urge Russia to use its influence with these groups to get them to release the observers, disarm and participate in a political process," Carney said.
Separatists confirmed that they detained the four observers, who have been missing since Monday.