WASHINGTON, July 23 (Xinhua) -- A Pentagon spokesman on Wednesday said that Russia continues to arm and train separatists in eastern Ukraine near the border area and has dispatched more than 100 additional pieces of military equipment across the border in recent days.
"We know that they sent, for example, last week a column of over 100 vehicles which included tanks, artillery, multiple launch rocket systems," Steve Warren said, adding that these actions are consistent with Moscow's behavior in eastern Ukraine for several months.
On the international investigation into the crash of the Malaysian Airlines jet in eastern Ukraine last week, which killed all 298 people on board, Warren said the United States does not know who, in particular, fired the missile that blew Malaysia airliner MH17 out of the sky, but Russia must be involved.
"There is no question that the Russians are backing these separatists and they bear responsibility ... for what happens in eastern Ukraine," he said. Moscow, he added, continues to maintain as many as 12,000 troops along the Ukrainian border.
Warren said he was aware of fresh reports from Ukraine that two Ukrainian fighter jets were shot down Wednesday over an area held by separatists.
"We are continuing to work with the Ukrainians and through our own channels to determine the exact circumstances surrounding that incident," he said.
On Monday, U.S. President Barack Obama noted in a speech that Russia has direct responsibility to compel the separatists to cooperate with the investigation.
Russia has denied any involvement in the incident and demanded the United States make public its relevant satellite pictures.