KIEV, Ukraine (CNN) -

Pro-Russian separatists struck two helicopters as well as a jet with portable air defense systems Wednesday in the Luhansk region of Ukraine.

A source within the Ukrainian military confirmed the statement by the "South-East Army," which claims the group downed an Ukrainian Su-25 military jet and a Mi-24 helicopter.

Another Ukrainian Mi-24 helicopter was struck, also in the Luhansk region, but it is unclear as to whether that aircraft crashed.

On Sunday, a Ukrainian fighter jet was shot down in the Luhansk region, Leonid Matyuhin, the spokesman for Ukraine's counterterrorist operation, told CNN.

The pilot managed to eject and is safe, Ukrainian state media reported.

The ongoing fighting -- sparked last year with by political crisis over whether Ukraine would seek closer ties with Europe or Russia -- has left more than 2,000 people dead and just under 5,000 wounded in eastern Ukraine since mid-April, according to estimates from U.N. officials.

The United States and the European Union have applied steadily increasing sanctions against Russian officials, banks and other interests since March, when Russia annexed the Black Sea Ukrainian peninsula of Crimea.

Russia's move came a month after Ukraine's parliament ousted pro-Moscow President Viktor Yanukovych.

Yanukovych left office after violent protests against his government in the capital, Kiev.

Those protests were motivated in part by his decision to back out of a trade deal with the European Union in favor of closer ties with Russia.