A Ukrainian fighter jet has been shot down by a Russian plane and troops have been fired upon by missiles from a village inside Russia, a spokesman for Ukraine's Security Council says.
The alleged episodes mark what Ukraine says is mounting evidence that Moscow is directly supporting the separatist insurgents in eastern Ukraine who have been seen to have substantial quantities of powerful weapons in recent weeks.
Security Council spokesman Andrei Lysenko said the pilot of the Sukhoi-25 jet hit by the air-to-air missile was forced to bail out. He said the rockets launched at Ukrainian troops were fired from the Russian village of Kuibyshevo.
Meanwhile, pro-Russian rebels claimed responsibility for strikes 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 safely.
Moscow denies Western charges that it is supporting the separatists or sowing unrest in its neighbour.
Earlier this week, Ukraine said a military transport plane was shot down on Monday by a missile fired from Russian territory. Security service chief Valentyn Nalyvaichenko said he had "unconditional evidence" that Russia was involved in downing that craft.
The rebels are known to possess portable anti-aircraft rocket launchers, but Ukrainian officials say that kind of weapon would have been unable to reach the plane at the altitude at which it was flying on Monday. Aviation experts, however, have questioned whether the stricken transport plane was flying at the altitude Ukrainian officials claimed.
Although the pro-Russia insurgents fighting the government in Kiev suffered a major setback earlier this month when they abandoned their stronghold in the city of Slovyansk, they still appear well-supplied militarily and have inflicted heavy losses on government troops.
Ukraine's border service said it has evidence that five Grad multiple-rocket launchers and two armoured personnel carriers were brought across the border on Wednesday from Russia.