An Air Force fighter jet has been shot down by an air-to-air missile fired from a Russian plane, a spokesman for Ukraine's Security Council said Thursday.
Andrei Lysenko also said Ukrainian troops had been fired upon by missiles from a village just inside Russia.
- Ukraine says plane shot down by rocket from Russia
- Russia calls new U.S., EU sanctions 'attempt to take vengeance'
Officials in Kyiv have recently accused Russia's armed forces of being directly implicated in attacks on Ukrainian troops battling an insurgency near the border.
Lysenko said in a televised briefing that the pilot of the Sukhoi-25 jet that was hit on Wednesday evening was forced to bail out after his jet was shot down. He provided no further details.
Pro-Russia rebels, meanwhile, claimed responsibility for strikes Wednesday on two Ukrainian Sukhoi-25 jets.
The Defence Ministry said the second jet was hit by a portable surface-to-air missile, but added the pilot was unscathed and managed to land his plane safely.
Moscow denies Western charges that it is supporting the separatists in Ukraine or sowing unrest in its neighbour.
Russia's Defence Ministry denied that it had shot down the plane and called the accusations "absurd," Reuters reported.
"It is absurd, just like all the previous accusations from Kyiv's leadership against Russia's Defence Ministry," Reuters quoted a ministry spokesman as saying.
Russia's United Nations ambassador said Russia did not shoot down the plane, Reuters reported. "We didn't do it," said Vitaly Churkin when asked about the incident by reporters.
On Monday, Ukraine said one of its military transport planes carrying eight people was shot down by a missile fired from Russian territory. Security Service chief Valentyn Nalyvaichenko said he had "unconditional evidence" that Russia was involved in downing the craft.
Rebels claimed to have shot that plane down.
U.S. imposes tougher sanctions
The U.S. slapped tougher sanctions against Russia on Wednesday for its actions in Ukraine, prompting a strong reaction Thursday from Russian President Vladimir Putin, who said they will stalemate bilateral relations and hurt not only Russian, but also American businesses.
Russia's benchmark MICEX was down 2.6 per cent in early afternoon trading Thursday upon news of the sanctions while Russia's biggest oil company, Rosneft, was nearly five per cent down.
The U.S. sanctions target two major Russian energy firms including Rosneft, a pair of powerful financial institutions, eight weapons firms and four individuals.
The U.S. penalties, however, stopped short of the most stringent actions the West has threatened, which would fully cut off key sectors of Russia's oil-dependent economy. But officials said those steps were still on the table if Russia fails to abide by the West's demands to stop its support for the pro-Russia insurgents.