A Ukrainian air force jet was shot at and struck down late Wednesday by a missile fired from a Russian plane, a spokesperson for Ukraine’s Security Council said according to Associated Press, or AP.

Andrei Lysenko, the Security Council spokesperson, said in a televised address that the jet was fired at from a Russian plane in flight, adding that Ukrainian troops were also attacked by missiles from a village across the Russian border. The Ukrainian jet was a Russian-made Sukhoi-25, according to AP.  Pro-Russian rebels claimed responsibility for shooting down two Sukhoi-25 jets on Wednesday.

The attack follows repeated accusations by Ukraine that Russian forces are supplying arms to separatist rebels in the east, but Moscow has denied the claims. On Monday, the administration in Kiev had said that a missile from inside Russian territory shot down a Ukrainian military plane, carrying eight people, killing all of them. Valentyn Nalyvaichenko, Ukraine’s security service chief had said at the time that the administration had “unconditional evidence” that Moscow was involved in the act, according to AP, but pro-Russian rebels claimed responsibility for the attack later.

The failure of a recent cease-fire between the two countries has led to a new round of sanctions imposed against Russia by the U.S. and the European Union, who have accused Russia of not making an effort to de-escalate violence in the region. Russia reacted to U.S. sanctions by stating that the move would affect bilateral ties and business between both countries.

"We consider the new round of American sanctions against Russia as a primitive attempt to take vengeance for the fact that events in Ukraine are not playing out to the tune of the script of Washington," Russia’s foreign ministry said, in a statement Thursday, according to AP.