A Ukrainian serviceman was reportedly shot and killed and another injured in Crimea Tuesday, just hours after Russia formally moved to annex the territory. Global leaders on alert in case the situation escalates, as it has been feared for weeks that an act of violence like this could spark a larger fight.

Ukraine's military spokesman Vladislav Seleznyov said it's not yet clear who killed the officer, but identified the attackers as "unknown forces, fully equipped and their faces covered." But Ukrainian Prime Minister Arseniy Yatseniuk, blamed the attack on Russia, saying the country had committed a war crime by firing on Ukrainian troops:  

The conflict is moving from a political one to a military one because of Russian soldiers. Today, Russian soldiers began shooting at Ukrainian servicemen and this is a war crime without any expiry under a statute of limitations. 

Eyewitnesses also reported the movement of Russian forces in Crimea: 

Russia is maintaining its innocence per usual, according to ABC's Alexander Marquardt, even claiming they (or their local "defense fighters") were the ones fired upon:

The violence comes just hours after Russia signed a treaty to annex Crimea and Putin said he wanted friendly relations with Ukraine. (He's also praised Ukraine's military for their restraint during the standoffs.) But the document basically means nothing to the international community at this point. The Guardian reports that according to White House press secretary Jay Carney, "Russia's attempt to annex a region of Ukraine illegally will never be recognized by the U.S. or the international community." The sentiment echoes what French President Francois Hollande, among others, said earlier today.