The crisis in Ukraine took another dramatic turn on Tuesday when Ukrainian security forces launched an operation against pro-Russian separatists in the eastern part of the country. Over the past week, separatists seized several administrative and security buildings throughout the eastern region, and in response the Ukrainian security forces took an airfield near the city of Kramatorsk, reportedly freeing the area from separatists.

The operation was preceded by a buildup of Ukrainian forces, fuel and supplies in Izyum, a city located about 50 kilometers (31 miles) northwest of Slovyansk and Kramatorsk. From Izyum, a mechanized force of reportedly 500 personnel advanced toward Slovyansk and Kramatorsk and set up checkpoints to isolate and contain the area. Afterward, the SBU, Ukraine's security service, conducted a direct action raid on the airfield.

Currently, it is unclear whether Ukrainian security forces will launch operations elsewhere in the region, though the government acknowledged that its planned anti-terrorist operation would be slow and gradual. In any case, the airfield was a logical target for Kiev, which may have reclaimed it in anticipation of its worst-case scenario: an invasion by Russia. (Typically, when Russia intervenes in another country, it supports protests and then supports informal militias before invading militarily.)

Notably, there are not many more areas like the airfield, which lies outside urban areas and is lightly defended. Going into the heart of eastern cities and digging out armed separatists from seized buildings would be more difficult if they put up a concerted defense.

Despite the apparent success of this operation, several things should worry the Ukrainian government and its security apparatus as it tries to counter eastern separatists. First, armed pro-Russian groups continue to entrench themselves throughout the region and continue to occupy buildings in nearly a dozen cities in eastern Ukraine. Second, the Russian military remains alert, with nearly 40,000 Russian troops ready for rapid mobilization along the border with eastern Ukraine. While a formal Russian military intervention into mainland Ukraine entails significant logistical and political constraints, Ukraine cannot be sure that Moscow would opt out of invading.

But perhaps the most worrisome prospect of Ukraine's security situation comes not from Russia or pro-Russian forces but from inside the Ukrainian government itself. On Tuesday, presidential candidate Yulia Timoshenko, whose Fatherland party holds many posts in the current Cabinet, announced her party would create special mobilization centers for a "National Resistance Movement" — a designation for militia units. To explain her decision, Timoshenko said that "power structures and the army cannot cope fully with the tasks because the security forces and the army were plundered," adding that such groups had already begun to form in Kharkiv, Zaporozhye and Dnipropetrovsk.

Though Timoshenko said her party would coordinate the resistance movement's activities with the Defense and Interior ministries, it is unclear whether it can effectively do so. During the EuroMaidan movement, militias from the Right Sector initially coordinated with the Fatherland and other opposition parties. Following the overthrow of former Ukrainian President Viktor Yanukovich, some elements of Right Sector were incorporated into the security apparatus while others continue to resist the government. In the meantime, militias from the pro-Russian side sprang up in reaction to those that formed in the EuroMaidan movement. The formation of yet another armed and loosely regulated militia group could further complicate an already chaotic situation on the ground.

The proliferation of militias aside, there is also a branding war taking place, in which Russia refers to overtly U.S.-backed Ukrainian forces as "fascist-terrorists" just as the West refers to Russian-backed forces as "separatist-terrorists." That Ukrainian forces are willing to risk violence plays into Russia's hands; the situation can deteriorate quickly, and the military composure the United States has praised could easily break down.

All this commotion in the east could also disrupt planned talks with the United States, Russia, the European Union and Ukraine in Geneva on Thursday. If military operations continue, Russia may be unwilling to resolve the crisis diplomatically. The prospects for effective negotiations over the crisis currently appear to be weakening rather than strengthening.