Brendan Hoffman/Getty Images

As-yet-unknown gunmen shot and gravely wounded the mayor of Ukraine's second-largest city, Kharkiv, in the back on Monday. The mayor, Hennady Kernes, is listed in "grave but stable" condition after a series of operations on his chest and abdomen. Kharkiv, a city of 1.5 million, is the only major population center in eastern Ukraine where the pro-Moscow insurgency has had little success.

The Kernes shooting kicked off a day of violence in eastern Ukraine. Pro-Russia militants seized a government building in yet another town, Kostyantynivka, and hundreds of men in military fatigues shouting "Russia!" attacked a 1,000-strong rally for Ukrainian unity in Donetsk using batons, bricks, iron bars, and stun grenades to beat and injure dozens of peaceful marchers. A similar clash occurred in Kharkiv on Sunday, with militants attacking a pro-unity march by fans of rival soccer teams.

Pro-Moscow militants are also still holding seven European observers from the Organization for Security and Cooperation in Europe and five Ukrainian security personnel who were accompanying them. In what passes for good news, one of the OSCE observers, a Swede, was released for health reasons. And Russia's defense chief told U.S. Defense Secretary Chuck Hagel on the phone that Russia won't invade Ukraine, according to the Pentagon. That's good, though if I were in Ukraine I'd want that in writing, signed by Russian President Vladimir Putin.