Malaysian Passenger Jet Went Down In One Of The Last Separatist Strongholds

The destruction of a Malaysian Airlines plane took place near Donetsk, site of a self-proclaimed pro-Russian "people's republic" that is one of the last major pro-Moscow holdouts in Ukraine's restive east.

An adviser to the Ukraine Interior Minister has alleged that pro-Russia separatists shot down the passenger plane with a Russian-made Buk ground-to-air missile system.

The rebels have been remarkably successful at shooting down Ukrainian government aircraft, and the separatists in the area reportedly commandeered a set of the Buk system as of last month.

Furthermore, The Interpreter reports the Ukrainian journalist Roman Bochkala and an AP journalist have seen separatists with the BUK system.

Over the past 24 hours, the Ukrainian government accused Russia of shooting down one of its fighter jets. A transport plane was shot down earlier in the week as well.

For the rebels, this capability represented a potential remaining advantage in the face of a situation that seemed to be rapidly turning on them.

Hannah Thoburn, a Eurasia analyst at the Washington, DC-based Foreign Policy Initiative, explained to Business Insider that the pro-Russian forces have suffered a series of setbacks in recent days. Most notable was the Ukrainian military's successful campaign to re-take Slaviansk, another self-declared pro-Moscow enclave.

With Slaviansk gone, the Donetsk rebels - who are led by an apparent Russian intelligence operative who holds Russian citizenship - are increasingly wondering at the direction of their campaign against Kiev.

"There's been a sense that the Ukrainians have really gained the upper hand. They've gained some momentum, and are feeling much more confident in themselves," says Thoburn. "The rebels lost some of the momentum they initially had."

And the latest incident didn't happen far from the heavily-contested city of Luhansk, another front in what was an increasingly tense theater even before the Malaysian plane was shot down:

Now, if it's proven that they shot down the Malaysia plane, it could be the trigger for a major escalation that neither Russian president Vladimir Putin nor the remaining rebel leaders might have been bargaining for.