A Ukrainian soldier stands guard during a field training exercise at Rapid Trident 2012 in Yavoriv. (Flickr/U.S. Army Europe)

A Ukrainian servicemen has been shot dead in an attack on a military base in the Crimean capital of Simerfol.

There have been conflicting reports about the victim, but the attackers have been described as "armed, masked men" by both Al-Jazeera and Reuters.

The attack comes hours after Russian President Vladimir Putin formally signed a treaty annexing the Crimean peninsula in the naval port town of Sevastopol, essentially absorbing the once autonomous region into the Russian Federation. The treaty itself comes less than 48 hours after a contentious and disputed referendum, polling Crimean residents on whether or not to secede from Ukraine.

READ MORE: Crimea Voters Support Joining Russia In Landslide Referendum

Western powers, completely rebuffed by Putin, are now tasked with generating new options after lukewarm sanctions appear to have detered little. Stronger sanctions would be "complicated, and not without negative implications for Western governments," according to BBC News Business.

Amidst the escalating crisis, Vice President Biden touched down in Poland today, hoping to reassure Eastern European countries that NATO will stand by its commitment to protect nations from further Russian aggression. But the Vice President reiterated that the administration's immediate strategy is to attack Putin with sanctions and not with troops, according to The Los Angeles Times.

Reach editor Will Federman here. Follow him on Twitter.