Valentyn Nalyvaichenko, head of Ukraine's security service SBU, said evidence suggested a military plane shot down Monday over the Luhansk region, near the Russian border, was flying too high for surface-to-air missiles to strike it.
The Ukrainian presidential website quoted Defense Minister Valeriy Heletey as saying, "The plane was struck by another, more powerful projectile that was probably launched from the territory of the Russian Federation."
The An-26 plane was carrying eight people, as well as food and supplies, when it crashed. Those aboard the plane survived, but Pro-Russian separatists said Monday four crew members were taken prisoner.
Nalyvaichenko said the evidence of Russia's involvement would be presented to Ukrainian President Petro Poroshenko, then made public.
Gen. Mykhaylo Koval, deputy secretary of Ukraine's National Security and Defense Council, said in a television interview that "Ukraine, as never before, is on the threshold of large-scale aggression by our northern neighbor."
At the European Union in Brussels Tuesday, Ukraine's EU representative Kostyantyn Yeliseyev presented what he called evidence of Russian support of pro-Russian separatists in Ukraine. "Incidents of Russia's interference have become more daring," he said. "EU member countries should place international law, shared democratic principles and common sense above their business and energy interests."
Yeliseyev suggested tighter economic sanctions be drawn against Russia.